Put latest AMIs into alpha channel
Put latest AMIs into alpha channel

Including trying out the stretch image for 1.9 and later.  (We have
jessie & stretch images for 1.8, but jessie should stay as the default
for 1.8.)

andrewsykim/kops,aledbf/kops,aledbf/kops,gambol99/kops,kubernetes/kops,gambol99/kops,robinpercy/kops,justinsb/kops,tsupertramp/kops,mad01/kops,aledbf/kops,mad01/kops,chrislovecnm/kops,blakebarnett/kops,kubernetes/kops,tsupertramp/kops,andrewsykim/kops,gambol99/kops,aledbf/kops,mad01/kops,robinpercy/kops,chrislovecnm/kops,blakebarnett/kops,justinsb/kops,andrewsykim/kops,blakebarnett/kops,robinpercy/kops,kubernetes/kops,blakebarnett/kops,justinsb/kops,chrislovecnm/kops,tsupertramp/kops,tsupertramp/kops,mad01/kops,robinpercy/kops,chrislovecnm/kops,andrewsykim/kops,gambol99/kops