Move conformance image to debian:stretch-slim
Move conformance image to debian:stretch-slim

Pros:
- really small image (see comparison below)
- we need to get rid of hyperkube in upcoming releases

```
davanum@cloudshell:~$ docker images
REPOSITORY                                       TAG                 IMAGE ID            CREATED             SIZE
debian                                           stretch-slim        4e6990ebcef5        4 days ago          55.3MB
gcr.io/google-containers/debian-hyperkube-base   0.12.1              a46476511725        13 months ago       393MB
```
jessfraz/kubernetes,pires/kubernetes,ravisantoshgudimetla/kubernetes,roberthbailey/kubernetes,ravilr/kubernetes,spzala/kubernetes,xlgao-zju/kubernetes,johscheuer/kubernetes,iameli/kubernetes,jessfraz/kubernetes,tcnghia/kubernetes,brendandburns/kubernetes,krmayankk/kubernetes,iameli/kubernetes,tomzhang/kubernetes,ravisantoshgudimetla/kubernetes,tallclair/kubernetes,erwinvaneyk/kubernetes,BenTheElder/kubernetes,alejandroEsc/kubernetes,ping035627/kubernetes,csrwng/kubernetes,jdef/kubernetes,dixudx/kubernetes,zhangmingld/kubernetes,x13n/kubernetes,andrewsykim/kubernetes,tengqm/kubernetes,soltysh/kubernetes,verult/kubernetes,lojies/kubernetes,iameli/kubernetes,andrewrynhard/kubernetes,weiwei04/kubernetes,coolsvap/kubernetes,chrislovecnm/kubernetes,cmluciano/kubernetes,mengqiy/kubernetes,cofyc/kubernetes,thockin/kubernetes,erwinvaneyk/kubernetes,pires/kubernetes,hex108/kubernetes,jingxu97/kubernetes,Acidburn0zzz/kubernetes,saad-ali/kubernetes,nak3/kubernetes,kitt1987/kubernetes,nikhita/kubernetes,kubernetes/kubernetes,k82/kubernetes,andrewsykim/kubernetes,bparees/kubernetes,yarntime/kubernetes,bparees/kubernetes,mengqiy/kubernetes,feiskyer/kubernetes,tengqm/kubernetes,coolsvap/kubernetes,coolsvap/kubernetes,joelsmith/kubernetes,shyamjvs/kubernetes,zetaab/kubernetes,mengqiy/kubernetes,jdef/kubernetes,kpgriffith/kubernetes,nak3/kubernetes,andrewrynhard/kubernetes,stevesloka/kubernetes,cblecker/kubernetes,tomzhang/kubernetes,luxas/kubernetes,maciaszczykm/kubernetes,sanjeevm0/kubernetes,PiotrProkop/kubernetes,cblecker/kubernetes,enj/kubernetes,soltysh/kubernetes,dixudx/kubernetes,bparees/kubernetes,cblecker/kubernetes,chestack/kubernetes,ravisantoshgudimetla/kubernetes,chestack/kubernetes,mikedanese/kubernetes,k82cn/kubernetes,jessfraz/kubernetes,pwittrock/kubernetes,li-ang/kubernetes,fanzhangio/kubernetes,coolsvap/kubernetes,kpgriffith/kubernetes,spzala/kubernetes,fejta/kubernetes,sdminonne/kubernetes,kitt1987/kubernetes,andrewrynhard/kubernetes,mikedanese/kubernetes,weiwei04/kubernetes,ixdy/kubernetes,olivierlemasle/kubernetes,jingxu97/kubernetes,monopole/kubernetes,Lion-Wei/kubernetes,humblec/kubernetes,Acidburn0zzz/kubernetes,klaus1982/kubernetes,bparees/kubernetes,kevensen/kubernetes,andrewrynhard/kubernetes,fgimenez/kubernetes,shyamjvs/kubernetes,stevesloka/kubernetes,erwinvaneyk/kubernetes,krmayankk/kubernetes,sethpollack/kubernetes,dlorenc/kubernetes,gnufied/kubernetes,coolsvap/kubernetes,mengqiy/kubernetes,PiotrProkop/kubernetes,soltysh/kubernetes,ping035627/kubernetes,fejta/kubernetes,MHBauer/kubernetes,sdminonne/kubernetes,matthyx/kubernetes,PI-Victor/kubernetes,brendandburns/kubernetes,olivierlemasle/kubernetes,idvoretskyi/kubernetes,mikedanese/kubernetes,jackfrancis/kubernetes,yujuhong/kubernetes,zetaab/kubernetes,hex108/kubernetes,nak3/kubernetes,rrati/kubernetes,gnufied/kubernetes,ii/kubernetes,x13n/kubernetes,tomzhang/kubernetes,zhouhaibing089/kubernetes,MikeSpreitzer/kubernetes,tcnghia/kubernetes,csrwng/kubernetes,saad-ali/kubernetes,mfojtik/kubernetes,deads2k/kubernetes,Lion-Wei/kubernetes,enj/kubernetes,matthyx/kubernetes,kevensen/kubernetes,saad-ali/kubernetes,enj/kubernetes,kevensen/kubernetes,GulajavaMinistudio/kubernetes,du2016/kubernetes,kpgriffith/kubernetes,cofyc/kubernetes,tpepper/kubernetes,andrewsykim/kubernetes,kpgriffith/kubernetes,mboersma/kubernetes,chrislovecnm/kubernetes,mkumatag/kubernetes,BenTheElder/kubernetes,warmchang/kubernetes,kevensen/kubernetes,Clarifai/kubernetes,brendandburns/kubernetes,linux-on-ibm-z/kubernetes,Acidburn0zzz/kubernetes,Lion-Wei/kubernetes,du2016/kubernetes,openshift/kubernetes,sethpollack/kubernetes,iterion/kubernetes,fabriziopandini/kubernetes,Acidburn0zzz/kubernetes,jagosan/kubernetes,zhouhaibing089/kubernetes,cblecker/kubernetes,mboersma/kubernetes,idvoretskyi/kubernetes,saad-ali/kubernetes,johscheuer/kubernetes,mkumatag/kubernetes,ixdy/kubernetes,zhouhaibing089/kubernetes,cmluciano/kubernetes,BenTheElder/kubernetes,dixudx/kubernetes,zhangmingld/kubernetes,joelsmith/kubernetes,chestack/kubernetes,k82cn/kubernetes,csrwng/kubernetes,k82/kubernetes,Lion-Wei/kubernetes,zetaab/kubernetes,nckturner/kubernetes,warmchang/kubernetes,tpepper/kubernetes,GulajavaMinistudio/kubernetes,enj/kubernetes,jessfraz/kubernetes,ingvagabund/kubernetes,chestack/kubernetes,tallclair/kubernetes,cofyc/kubernetes,ping035627/kubernetes,JacobTanenbaum/kubernetes,jackfrancis/kubernetes,ingvagabund/kubernetes,xlgao-zju/kubernetes,cofyc/kubernetes,andrewsykim/kubernetes,pires/kubernetes,MikeSpreitzer/kubernetes,cofyc/kubernetes,verult/kubernetes,rnaveiras/kubernetes,weiwei04/kubernetes,mfojtik/kubernetes,MikeSpreitzer/kubernetes,aledbf/kubernetes,yarntime/kubernetes,mboersma/kubernetes,linux-on-ibm-z/kubernetes,micahhausler/kubernetes,thockin/kubernetes,tengqm/kubernetes,kevensen/kubernetes,nikhita/kubernetes,brendandburns/kubernetes,rrati/kubernetes,mYmNeo/kubernetes,stevesloka/kubernetes,ravilr/kubernetes,MHBauer/kubernetes,k82/kubernetes,carlory/kubernetes,fgimenez/kubernetes,x13n/kubernetes,dereknex/kubernetes,tcnghia/kubernetes,tomzhang/kubernetes,ravisantoshgudimetla/kubernetes,tengqm/kubernetes,feiskyer/kubernetes,JacobTanenbaum/kubernetes,jdef/kubernetes,ravilr/kubernetes,fanzhangio/kubernetes,dims/kubernetes,mfojtik/kubernetes,sanjeevm0/kubernetes,dims/kubernetes,johscheuer/kubernetes,dereknex/kubernetes,mfojtik/kubernetes,cmluciano/kubernetes,zhangmingld/kubernetes,rnaveiras/kubernetes,luxas/kubernetes,rafax/kubernetes,rrati/kubernetes,Clarifai/kubernetes,lojies/kubernetes,ravilr/kubernetes,linux-on-ibm-z/kubernetes,micahhausler/kubernetes,zhangmingld/kubernetes,tcnghia/kubernetes,cmluciano/kubernetes,mboersma/kubernetes,ixdy/kubernetes,weiwei04/kubernetes,mahak/kubernetes,brendandburns/kubernetes,fejta/kubernetes,mahak/kubernetes,fejta/kubernetes,maciaszczykm/kubernetes,mfojtik/kubernetes,idvoretskyi/kubernetes,deads2k/kubernetes,liggitt/kubernetes,csrwng/kubernetes,matthyx/kubernetes,lojies/kubernetes,tomzhang/kubernetes,wongma7/kubernetes,deads2k/kubernetes,ixdy/kubernetes,klaus1982/kubernetes,fgimenez/kubernetes,mkumatag/kubernetes,tomerf/kubernetes,brendandburns/kubernetes,wongma7/kubernetes,jagosan/kubernetes,wanghaoran1988/kubernetes,gnufied/kubernetes,dixudx/kubernetes,PiotrProkop/kubernetes,nikhita/kubernetes,yarntime/kubernetes,nckturner/kubernetes,mosoft521/kubernetes,johscheuer/kubernetes,andrewrynhard/kubernetes,monopole/kubernetes,iameli/kubernetes,iterion/kubernetes,fabriziopandini/kubernetes,humblec/kubernetes,kubernetes/kubernetes,thockin/kubernetes,dereknex/kubernetes,linux-on-ibm-z/kubernetes,mboersma/kubernetes,andrewsykim/kubernetes,roberthbailey/kubernetes,luxas/kubernetes,maciaszczykm/kubernetes,li-ang/kubernetes,kitt1987/kubernetes,stevesloka/kubernetes,tomerf/kubernetes,openshift/kubernetes,luxas/kubernetes,Clarifai/kubernetes,jsafrane/kubernetes,tomerf/kubernetes,iameli/kubernetes,mboersma/kubernetes,kpgriffith/kubernetes,ravilr/kubernetes,verb/kubernetes,MHBauer/kubernetes,nckturner/kubernetes,kubernetes/kubernetes,idvoretskyi/kubernetes,verb/kubernetes,saad-ali/kubernetes,huangjiuyuan/kubernetes,nckturner/kubernetes,dims/kubernetes,spzala/kubernetes,klaus1982/kubernetes,andrewrynhard/kubernetes,yujuhong/kubernetes,tpepper/kubernetes,gnufied/kubernetes,cmluciano/kubernetes,bparees/kubernetes,ii/kubernetes,dims/kubernetes,sanjeevm0/kubernetes,maciaszczykm/kubernetes,chestack/kubernetes,lojies/kubernetes,jdef/kubernetes,cmluciano/kubernetes,carlory/kubernetes,verb/kubernetes,k82cn/kubernetes,ping035627/kubernetes,mboersma/kubernetes,thockin/kubernetes,carlory/kubernetes,yarntime/kubernetes,pwittrock/kubernetes,joelsmith/kubernetes,soltysh/kubernetes,fanzhangio/kubernetes,tpepper/kubernetes,jackfrancis/kubernetes,rafax/kubernetes,feiskyer/kubernetes,alejandroEsc/kubernetes,GulajavaMinistudio/kubernetes,johscheuer/kubernetes,JacobTanenbaum/kubernetes,aledbf/kubernetes,nckturner/kubernetes,saad-ali/kubernetes,rafax/kubernetes,matthyx/kubernetes,fabriziopandini/kubernetes,tpepper/kubernetes,ravisantoshgudimetla/kubernetes,ingvagabund/kubernetes,yujuhong/kubernetes,kubernetes/kubernetes,lojies/kubernetes,x13n/kubernetes,kevin-wangzefeng/kubernetes,xychu/kubernetes,tcnghia/kubernetes,wanghaoran1988/kubernetes,jessfraz/kubernetes,humblec/kubernetes,xychu/kubernetes,Lion-Wei/kubernetes,Clarifai/kubernetes,dereknex/kubernetes,rrati/kubernetes,fanzhangio/kubernetes,x13n/kubernetes,rnaveiras/kubernetes,kevin-wangzefeng/kubernetes,mosoft521/kubernetes,du2016/kubernetes,warmchang/kubernetes,wanghaoran1988/kubernetes,sanjeevm0/kubernetes,mikebrow/kubernetes,monopole/kubernetes,xlgao-zju/kubernetes,verult/kubernetes,humblec/kubernetes,linux-on-ibm-z/kubernetes,mosoft521/kubernetes,mengqiy/kubernetes,tomzhang/kubernetes,pires/kubernetes,sdminonne/kubernetes,luxas/kubernetes,yujuhong/kubernetes,wongma7/kubernetes,xlgao-zju/kubernetes,verb/kubernetes,iterion/kubernetes,k82cn/kubernetes,erwinvaneyk/kubernetes,tomerf/kubernetes,zetaab/kubernetes,mahak/kubernetes,ping035627/kubernetes,xychu/kubernetes,chrislovecnm/kubernetes,mfojtik/kubernetes,zetaab/kubernetes,chrislovecnm/kubernetes,warmchang/kubernetes,nikhita/kubernetes,tallclair/kubernetes,deads2k/kubernetes,yarntime/kubernetes,openshift/kubernetes,zetaab/kubernetes,mYmNeo/kubernetes,k82/kubernetes,carlory/kubernetes,ixdy/kubernetes,shyamjvs/kubernetes,MikeSpreitzer/kubernetes,krmayankk/kubernetes,dereknex/kubernetes,k82cn/kubernetes,pwittrock/kubernetes,jdef/kubernetes,rafax/kubernetes,ravisantoshgudimetla/kubernetes,olivierlemasle/kubernetes,idvoretskyi/kubernetes,hex108/kubernetes,ii/kubernetes,mikedanese/kubernetes,mahak/kubernetes,matthyx/kubernetes,dereknex/kubernetes,hex108/kubernetes,tallclair/kubernetes,idvoretskyi/kubernetes,huangjiuyuan/kubernetes,jagosan/kubernetes,pires/kubernetes,sethpollack/kubernetes,mboersma/kubernetes,BenTheElder/kubernetes,sdminonne/kubernetes,spzala/kubernetes,fejta/kubernetes,yujuhong/kubernetes,kitt1987/kubernetes,nak3/kubernetes,ixdy/kubernetes,PI-Victor/kubernetes,dlorenc/kubernetes,wanghaoran1988/kubernetes,liggitt/kubernetes,pwittrock/kubernetes,BenTheElder/kubernetes,mikebrow/kubernetes,ingvagabund/kubernetes,maciaszczykm/kubernetes,mahak/kubernetes,feiskyer/kubernetes,verult/kubernetes,tengqm/kubernetes,joelsmith/kubernetes,roberthbailey/kubernetes,jsafrane/kubernetes,aledbf/kubernetes,aledbf/kubernetes,rrati/kubernetes,jsafrane/kubernetes,sethpollack/kubernetes,verb/kubernetes,du2016/kubernetes,thockin/kubernetes,stevesloka/kubernetes,mkumatag/kubernetes,PI-Victor/kubernetes,tcnghia/kubernetes,mosoft521/kubernetes,GulajavaMinistudio/kubernetes,Clarifai/kubernetes,warmchang/kubernetes,joelsmith/kubernetes,huangjiuyuan/kubernetes,ingvagabund/kubernetes,micahhausler/kubernetes,carlory/kubernetes,wanghaoran1988/kubernetes,du2016/kubernetes,liggitt/kubernetes,roberthbailey/kubernetes,fgimenez/kubernetes,ii/kubernetes,fgimenez/kubernetes,andrewsykim/kubernetes,tomzhang/kubernetes,klaus1982/kubernetes,pwittrock/kubernetes,aledbf/kubernetes,dlorenc/kubernetes,pires/kubernetes,Acidburn0zzz/kubernetes,tpepper/kubernetes,olivierlemasle/kubernetes,pwittrock/kubernetes,xychu/kubernetes,cblecker/kubernetes,mYmNeo/kubernetes,MHBauer/kubernetes,alejandroEsc/kubernetes,sdminonne/kubernetes,nak3/kubernetes,erwinvaneyk/kubernetes,xlgao-zju/kubernetes,mikedanese/kubernetes,jackfrancis/kubernetes,enj/kubernetes,kevin-wangzefeng/kubernetes,krmayankk/kubernetes,mikebrow/kubernetes,jagosan/kubernetes,alejandroEsc/kubernetes,rnaveiras/kubernetes,mosoft521/kubernetes,fabriziopandini/kubernetes,sethpollack/kubernetes,weiwei04/kubernetes,nak3/kubernetes,johscheuer/kubernetes,chrislovecnm/kubernetes,wongma7/kubernetes,mikebrow/kubernetes,olivierlemasle/kubernetes,weiwei04/kubernetes,JacobTanenbaum/kubernetes,micahhausler/kubernetes,stevesloka/kubernetes,liggitt/kubernetes,dixudx/kubernetes,kitt1987/kubernetes,zhouhaibing089/kubernetes,hex108/kubernetes,sanjeevm0/kubernetes,zhangmingld/kubernetes,ii/kubernetes,soltysh/kubernetes,krmayankk/kubernetes,PI-Victor/kubernetes,Lion-Wei/kubernetes,MHBauer/kubernetes,wanghaoran1988/kubernetes,openshift/kubernetes,tomzhang/kubernetes,MHBauer/kubernetes,zhangmingld/kubernetes,yujuhong/kubernetes,luxas/kubernetes,shyamjvs/kubernetes,fabriziopandini/kubernetes,k82/kubernetes,GulajavaMinistudio/kubernetes,fanzhangio/kubernetes,jingxu97/kubernetes,fgimenez/kubernetes,zhouhaibing089/kubernetes,jagosan/kubernetes,huangjiuyuan/kubernetes,MikeSpreitzer/kubernetes,mkumatag/kubernetes,PI-Victor/kubernetes,cofyc/kubernetes,monopole/kubernetes,openshift/kubernetes,xychu/kubernetes,chrislovecnm/kubernetes,xychu/kubernetes,yarntime/kubernetes,feiskyer/kubernetes,coolsvap/kubernetes,tomerf/kubernetes,sanjeevm0/kubernetes,alejandroEsc/kubernetes,iterion/kubernetes,deads2k/kubernetes,mikebrow/kubernetes,wongma7/kubernetes,iterion/kubernetes,jdef/kubernetes,roberthbailey/kubernetes,kitt1987/kubernetes,Acidburn0zzz/kubernetes,jingxu97/kubernetes,erwinvaneyk/kubernetes,micahhausler/kubernetes,tomzhang/kubernetes,spzala/kubernetes,nikhita/kubernetes,kevin-wangzefeng/kubernetes,joelsmith/kubernetes,tallclair/kubernetes,tallclair/kubernetes,kubernetes/kubernetes,ingvagabund/kubernetes,monopole/kubernetes,kpgriffith/kubernetes,humblec/kubernetes,jsafrane/kubernetes,mYmNeo/kubernetes,jackfrancis/kubernetes,hex108/kubernetes,iterion/kubernetes,PI-Victor/kubernetes,shyamjvs/kubernetes,dlorenc/kubernetes,liggitt/kubernetes,fejta/kubernetes,rnaveiras/kubernetes,tomerf/kubernetes,li-ang/kubernetes,JacobTanenbaum/kubernetes,krmayankk/kubernetes,jingxu97/kubernetes,xlgao-zju/kubernetes,Clarifai/kubernetes,jsafrane/kubernetes,mYmNeo/kubernetes,verult/kubernetes,mYmNeo/kubernetes,x13n/kubernetes,csrwng/kubernetes,JacobTanenbaum/kubernetes,huangjiuyuan/kubernetes,PiotrProkop/kubernetes,PiotrProkop/kubernetes,li-ang/kubernetes,maciaszczykm/kubernetes,kevin-wangzefeng/kubernetes,huangjiuyuan/kubernetes,dims/kubernetes,gnufied/kubernetes,dlorenc/kubernetes,fanzhangio/kubernetes,dlorenc/kubernetes,verult/kubernetes,li-ang/kubernetes