Added container image tagging on quay.io with commit id on every merge,
when certain files but not the code are changed (docs, charts, etc.).
Previously we were building updated container images, adding tags and
uploading images onto quay.io only when the code has been changed. The
main reason for not re-building images for every single merged commit
was a long waiting time in Zuul `post` queue for a node (VM)
assignment for the job to run on.
With this change we will have image tag for every merged commit,
including documentation commits, and those tags would be added almost
immediately (within ~1 min), as job runs directly on Zuul and does not
wait in Zuul queue for a node (VM) assignment.
Change-Id: I9692947b74a16de0eb3e8100d30cd4310069abfe
9dcc0ae937