CI: pytest-timeout is not installed

[ZLLentz]

Expected Behavior

pytest-timeout is used throughout the test suite to help us in the case where a scan freezes so we can proceed to the rest of the test suite.

Current Behavior

In the CI, we don't have pytest-timeout installed:

  /home/travis/build/pcdshub/nabs/nabs/tests/test_plans.py:18: PytestUnknownMarkWarning: Unknown pytest.mark.timeout - is this a typo?  You can register custom marks to avoid this warning - for details, see https://docs.pytest.org/en/stable/mark.html

Possible Solution

Check the other repos and add pytest-timeout appropriately as a dev requirements

Context

Maybe one day the test suite will freeze out and be annoying