Improve concurrency of machine-based executor
This changes to create a machines only once! Instead of doing it twice in main loop.
Solves: https://gitlab.com/gitlab-org/gitlab-ci-multi-runner/issues/1563
This changes to create a machines only once! Instead of doing it twice in main loop.
Solves: https://gitlab.com/gitlab-org/gitlab-ci-multi-runner/issues/1563