generate-cert: allow for alternative paths
generate-cert: allow for alternative paths

Instead of hard coding kube-cert and /srv/kubernetes allow these to be
overwritten by environment variables.  / is immutable on some systems
and so /srv is not a possible location to store data.

ostrichops/kube-deploy,sp-borja-juncosa/kops,justinsb/kube-deploy,dacohen/kops,austinmoore-/kops,ostrichops/kube-deploy,luomiao/kops,justinsb/kops,zytek/kops,DualSpark/kops,luxas/kube-deploy,BradErz/kops,luomiao/kops,spacexnice/kube-deploy,blakebarnett/kops,mad01/kops,pdh/kops,aledbf/kops,BradErz/kops,pdh/kops,reactiveops/kops,dacohen/kops,chrislovecnm/kops,sp-borja-juncosa/kops,andrewsykim/kops,MadDogTechnology/kops,tsupertramp/kops,chrislovecnm/kops,ikropotov/kops,sp-borja-juncosa/kops,DualSpark/kops,dacohen/kops,andrewsykim/kops,gambol99/kops,kubernetes/kops,pdh/kops,tsupertramp/kops,isavin/kube-deploy,justinsb/kops,BradErz/kops,sp-borja-juncosa/kops,MadDogTechnology/kops,chrislovecnm/kops,dacohen/kops,faraazkhan/kops,tsupertramp/kops,krousey/kube-deploy,jnewland/kops,faraazkhan/kops,WillemMali/kops,kris-nova/kops,BradErz/kops,isavin/kube-deploy,spacexnice/kube-deploy,ikropotov/kops,aledbf/kops,luxas/kube-deploy,austinmoore-/kops,sethpollack/kops,WillemMali/kops,mad01/kops,aledbf/kops,ostrichops/kube-deploy,blakebarnett/kops,robinpercy/kops,mad01/kops,blakebarnett/kops,kubernetes/kops,leandrocr/kops,jnewland/kops,austinmoore-/kops,gambol99/kops,gambol99/kops,reactiveops/kops,aledbf/kops,zytek/kops,pdh/kops,WillemMali/kops,DualSpark/kops,sethpollack/kops,justinsb/kops,luxas/kube-deploy,zytek/kops,ikropotov/kops,justinsb/kube-deploy,robinpercy/kops,MadDogTechnology/kops,ikropotov/kops,kris-nova/kops,krousey/kube-deploy,chrislovecnm/kops,reactiveops/kops,tsupertramp/kops,leandrocr/kops,kris-nova/kops,ajitak/kube-deploy,robinpercy/kops,kubernetes/kops,luomiao/kops,leandrocr/kops,andrewsykim/kops,kris-nova/kops,leandrocr/kops,gambol99/kops,blakebarnett/kops,reactiveops/kops,mad01/kops,MadDogTechnology/kops,faraazkhan/kops,DualSpark/kops,justinsb/kube-deploy,jnewland/kops,andrewsykim/kops,spacexnice/kube-deploy,luomiao/kops,ajitak/kube-deploy,sethpollack/kops,faraazkhan/kops,zytek/kops,isavin/kube-deploy,robinpercy/kops,austinmoore-/kops,WillemMali/kops,sethpollack/kops