At present, the only mechanism we have for publishing a stable heat
container agent image through manual tagging. This PS aims to automate
this through the CI by only building them if they have not already been
published. This should allow us to keep better track of which commit was
used to build a given heat container agent image.
Story: 2007264
Task: 40045
Change-Id: Ifb80575c18a34584afddc8b83084702713a802b7
ff57593984