Replace nose with pytest as the testing engine?

[rbiswas4]

LSST is migrating to py.test as the test runner rather than unittest. Like nose, which we have been using in Twinkles and Monitor, py.test will work with tests written in the unittest framework as well. I think this is an attractive option, because of

• continued support to tests written in the unittest or nose framework
• New features (I believe) not present in nose, that enable writing tests which seem harder to do in nose, but with less boilerplate than unittest, which I often find excessive for simple tasks.

So, I think we have two things to get done

• [x] Create a branch with the changes to get pytest working. I will try to do this. This is in branch: https://github.com/DarkEnergyScienceCollaboration/Monitor/tree/change_testing_engine_to_pytest
• [ ] Decide on this thread if the branch should be merged to make pytest a default test runner, and whether we should start using pytest features.