Tag and push 'latest' version of gitlab/gitlab-runner-helper image

Merged Tomasz Maczukin requested to merge feature/add-latest-tag-for-helper-images into master

What does this MR do?

Adds the -latest version of image introduced in !420 (merged)

Why was this MR needed?

-latest versions of images will be used, for example, as default images for Kubernetes executor if an image marked with revision will be not found (please read https://gitlab.com/gitlab-org/gitlab-ci-multi-runner/merge_requests/425#note_20382762 for a reference)

Are there points in the code the reviewer needs to double check?

Does this MR meet the acceptance criteria?

  • Documentation created/updated
  • Tests
    • Added for this feature/bug
    • All builds are passing
  • Branch has no merge conflicts with master (if you do - rebase it please)

What are the relevant issue numbers?