make py.test find test files

pytest is able to run the nose tests, but it needs a bit of help to
find them. since it reads the tox.ini file, we just need to add a glob
pattern there.

py.test will also create __pycache__ directories. add them to
.gitignore.
Merge pull request #102 from brainbot-com/pytest-support

make py.test find test files