Revert "Disable orchestration for command tests"

This reverts commit 2d5fe0f8780c52cfada2512cf233cafd4da5cf05.
We should not include such a test-specific feature!
Revert "Add an option to disable orchestration based on Serf."

This reverts commit d6d03af40892692ed2f80b7367b3c8872c4c5343.
We should not include such a test-specific feature!
Don't run command tests if Serf is not installed globally.