Add more methods to unit test blacklist

This change adds more methods to the unit test blacklist so that we
can more easily avoid filesystem effects and subprocess interaction
in our unit tests.
Not exactly -- PR #30 is related to repatching things that have already been patched. The `_do_network_mocks` flag prevents specific things from being patched at all. 

The reason for doing this is: it's useful to patch out `Network` functionality by default since so many classes use it, but since we also want to test that patched code, in `NetworkTest`, we want to disable the patches just for that class.

I'm not in love with this mechanism so if you can think of an alternative approach that would be cleaner I would definitely be interested. :grimacing: