Scheduler-specific unit tests broken on master

[vkarak]

Commit that introduced the problem: a0abcd0. This appears if you run the test_scheduler.py alone. It doesn't appear if you run the whole suite together, because the module path is modified by some tests that are run prior to it.

[vkarak]

The problem didn't appear in the full suite, because test_cli.py changes the module path globally and does not restore it, and this one runs before test_schedulers.py.