Docker Builds from Git Tag

Docker Builds from Git Tag

Facilitates the creation of docker images from tags pushed to Gerrit,
which should remove the need to manually trigger 'tagged' builds.

Fixes a typo in the 'gerrit-trigger-tag-created' macro,
replaces 'RELEASE_VERSION' with 'GERRIT_REFNAME', and adds the
tag-trigger to docker builds.

Change-Id: I6d8f8f34b1c51d74bb98211dfae21c37cf9356fa
Signed-off-by: Trevor Bramwell <tbramwell@linuxfoundation.org>