builder: add a test for `ENV name` (without `=value`)
builder: add a test for `ENV name` (without `=value`)

Signed-off-by: Akihiro Suda <ea940da7e429af3d0d0c18296cabd0112a36bad5@lab.ntt.co.jp>

amatsus/docker,bearstech/moby,x1022as/docker,mike1729/docker,coreos/docker,x1022as/docker,noironetworks/docker,johnstep/moby-moby,yongtang/docker,amatsus/docker,resin-io/docker,yummypeng/docker,unclejack/docker,yosifkit/docker,cpuguy83/docker,KingEmet/docker,konstruktoid/docker-upstream,dims/docker,tmp6154/docker,haveatry/docker,kolyshkin/docker,jthelin/docker,allencloud/docker,madhanrm/docker,gnailuy/docker,imkin/moby,mikebrow/docker,shishir-a412ed/docker,tklauser/docker,laijs/docker,moby/moby,jlhawn/docker,mike1729/docker,docker/docker,flavio/docker,rancher/docker,kolyshkin/moby,thaJeztah/docker,jvanz/docker,naveed-jamil-tenpearls/moby,KingEmet/docker,ibuildthecloud/docker,SvenDowideit/docker,yosifkit/docker,pradipd/moby,whuwxl/docker,moul/docker,x1022as/docker,charleszheng44/moby,crosbymichael/docker,kolyshkin/moby,imkin/moby,cyphar/docker,mahak/docker,ibuildthecloud/docker,ndeloof/docker,cpuguy83/docker,pradipd/moby,PatrickLang/moby,ripcurld0/moby,konstruktoid/docker-1,maxamillion/docker,maxamillion/docker,paralin/docker,kojiromike/docker,docker/docker,flavio/docker,YuPengZTE/docker,estesp/docker,lixiaobing10051267/docker,nawawi/docker,jlhawn/docker,trebonian/docker,dims/docker,POLJM242/docker,jameszhan/docker,jameszhan/docker,yasiramin10p/moby,mikebrow/docker,yongtang/docker,KarthikNayak/docker,unclejack/docker,lixiaobing1/docker,nawawi/docker,jthelin/docker,thaJeztah/docker,mkumatag/docker,liaoqingwei/docker,nalind/docker,pramodhkp/moby,cpuguy83/docker,Mokolea/docker,dsheets/moby,sterchelen/docker,docker/docker,naveed-jamil-tenpearls/moby,dccurtis/docker,dsheets/moby,shishir-a412ed/docker,rhatdan/docker,tophj-ibm/docker,imkin/moby,ibuildthecloud/docker,SvenDowideit/docker,bearstech/moby,Ramzec/docker,yosifkit/docker,konstruktoid/docker-upstream,moby/moby,YuPengZTE/docker,ibuildthecloud/docker,unclejack/docker,jimjag/docker,YuPengZTE/docker,shhsu/docker,POLJM242/docker,allencloud/docker,rancher/docker,fcrisciani/docker,mikebrow/docker,bearstech/moby,PatrickLang/moby,miminar/docker,fcrisciani/docker,sterchelen/docker,paralin/docker,flavio/docker,charleszheng44/moby,tophj-ibm/moby,tonistiigi/docker,estesp/docker,justincormack/docker,dccurtis/docker,KingEmet/docker,SvenDowideit/docker,srust/docker,Ramzec/docker,crosbymichael/docker,dmcgowan/docker,moby/moby,KarthikNayak/docker,tophj-ibm/docker,dperny/docker,djs55/docker,laijs/docker,konstruktoid/docker-upstream,JMesser81/docker,scotttlin/docker,shishir-a412ed/docker,coolljt0725/docker,nalind/docker,scotttlin/docker,laijs/moby,lixiaobing1/docker,lixiaobing10051267/docker,whuwxl/docker,nawawi/docker,yasiramin10p/moby,madhanrm/docker,konstruktoid/docker-1,cyphar/docker,hqhq/moby,moby/moby,tmp6154/docker,yosifkit/docker,crosbymichael/docker,vdemeester/docker,shhsu/docker,charleszheng44/moby,raja-sami-10p/moby,danyalKhaliq10p/moby,hqhq/moby,mahak/docker,yummypeng/docker,rancher/docker,jimjag/docker,mixja/docker,konstruktoid/docker-1,JMesser81/docker,nalind/docker,pradipd/moby,maxamillion/docker,jvanz/docker,yongtang/docker,raja-sami-10p/moby,tophj-ibm/moby,KarthikNayak/docker,naveed-jamil-tenpearls/moby,moul/docker,pramodhkp/moby,nalind/docker,jimjag/docker,mahak/docker,srust/docker,trebonian/docker,laijs/moby,tonistiigi/docker,lixiaobing1/docker,Mokolea/docker,estesp/docker,rremer/moby,haveatry/docker,tophj-ibm/docker,Mokolea/docker,resin-io/docker,raja-sami-10p/moby,miminar/docker,srust/docker,mixja/docker,laijs/moby,jlhawn/docker,ripcurld0/moby,tmp6154/docker,ndeloof/docker,jvanz/docker,paralin/docker,yummypeng/docker,bonczj/moby-json-file-logger,jameszhan/docker,cyphar/docker,AkihiroSuda/docker,haveatry/docker,moul/docker,gnailuy/docker,kojiromike/docker,tonistiigi/docker,djs55/docker,noironetworks/docker,yasiramin10p/moby,liaoqingwei/docker,kolyshkin/docker,coolljt0725/docker,mixja/docker,mkumatag/docker,tklauser/docker,bonczj/moby-json-file-logger,konstruktoid/docker-upstream,miminar/docker,dccurtis/docker,rhatdan/docker,liaoqingwei/docker,madhanrm/docker,vdemeester/docker,trebonian/docker,noironetworks/docker,coreos/docker,thaJeztah/docker,djs55/docker,laijs/docker,AkihiroSuda/docker,Ramzec/docker,jwhonce/docker,bearstech/moby,duglin/docker,dperny/docker,mahak/docker,thaJeztah/docker,trebonian/docker,cpuguy83/docker,fcrisciani/docker,AkihiroSuda/docker,vdemeester/docker,justincormack/docker,paralin/docker,scotttlin/docker,tophj-ibm/moby,dsheets/moby,Ramzec/docker,kolyshkin/moby,duglin/docker,rremer/moby,rhatdan/docker,coolljt0725/docker,tklauser/docker,jimjag/docker,ibuildthecloud/docker,gnailuy/docker,flavio/docker,jwhonce/docker,moul/docker,nawawi/docker,ndeloof/docker,amatsus/docker,resin-io/docker,allencloud/docker,whuwxl/docker,AkihiroSuda/docker,dmcgowan/docker,rremer/moby,dmcgowan/docker,kojiromike/docker,johnstep/moby-moby,lixiaobing10051267/docker,jwhonce/docker,mike1729/docker,gnailuy/docker,justincormack/docker,JMesser81/docker,danyalKhaliq10p/moby,mkumatag/docker,sterchelen/docker,PatrickLang/moby,coreos/docker,Mokolea/docker,dims/docker,bonczj/moby-json-file-logger,johnstep/moby-moby,dperny/docker,hqhq/moby,shhsu/docker,duglin/docker,danyalKhaliq10p/moby,pramodhkp/moby,ripcurld0/moby