Test fixes/improvements

After this I get all tests to pass, except for the webdriver_testing
app.

Fixed video types tests to work now that we don't strip url params
from the video URL.  Also changed the way we matched some video types.
I think this is a simpler and cleaner way to check the extension.
Removed the video_urls test which is only tested the URL stripping
feature feature.

Fixed comments tests after the latest changes.

Fixed team video feeds import tests.

Fixed merged dfxp test.

Fix for reset_mocks() in test_utils.  The previous code wasn't
resetting the child mocks.

Added the nose-exclude package which makes it easy to skip a
particular app's tests.  Added unittest2 package which allows
babelsubs tests to be run.

Added nosetests.xml to the gitignore file.

Fixed test_settings.py file.