Fetches latest epoxy-images release tag for sync
Fetches latest epoxy-images release tag for sync

In sandbox and staging the variable cfImagesVersion should always be
"latest", but in production (mlab-oti) it needs to be the latest release
tag of the epoxy-images repository. This commit adds some very simple
logic to lookup the latest release tag and use that when operating the
mlab-oti project.

m-lab/epoxy,m-lab/epoxy