Introduce Test::Sanity::Version and a `sanity` pipeline stage
As discussed in #76 (closed), a pre-run check to ensure the docker
nightly image is reasonably up-to-date would be a useful sanity check before running the rest of the gitlab-qa suite.
Here we add
Test::Sanity::Version that will pull an image, inspect the version-manifest.json, and check if key components (initially gitlab-rails and gitlab-shell) are recent.
Additionally we extend the CI pipeline to add a
sanity stage, and call Test::Sanity::Version against CE and EE nightly docker images.
Closes #76 (closed)