Build and push QA image on auto-deploy tags

Executes the Docker-QA job on builds with auto-deploy tags as well as other tags.

It modifies the qa:push:staging task to detect if the current build is an auto-deploy build. If so, it builds an image with a tag that includes the GitLab semver major and minor components plus the commit SHA. This allows gitlab-qa to figure out which image to pull using only the info returned from the version API.

This means that the docker image tags for auto-deploy builds will look like, e.g.: 12.0-3a5f14fef4e. This format is used rather than the full auto-deploy tag because gitlab-qa can't get the full tag from the version API, just the version and commit SHA.

There's also a gitlab-qa MR to go with this one: gitlab-qa!252 (merged)

This fixes the failures of QA staging tests. See: gitlab-org/quality/staging#56 (closed)