Added --cpus option support.

Closed username-removed-15146 requested to merge sashk/gitlab-ci-multi-runner:issue2101 into master

What does this MR do?

Adds CPUS option for docker runner.

Why was this MR needed?

Adds support for the --cpus option available in Docker 1.13. This allows limit number of CPUs available to each docker container.

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?