Fix "unit tests" random failures

What does this MR do?

Fixes randomly failing unit tests step in Runner's test suite.

Why was this MR needed?

The unit tests step is randomly failing. Failures are caused mainly by accessing external resources and data races during tests. Please fallow #1834 (closed) for reference.

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

Go chanels operations in executors/docker/machine/provider_test.go .

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?

Fixes #1834 (closed)