Previously when containers were added to the upstream kolla project or
added to our container list, the container build process might try and
build them when we execute kolla-build. This change adds a image_source
parameter that is used to understand when we should and should not
attempt to build the container with kolla witht he 'overcloud container
image build' command.
Change-Id: I82d6e09c856f78c0b29d7324c59b5e00bf5ae04d
Closes-BUg: #1801969