2587: Fix resolve_ownership method

resolve_ownership should handle VideoURL objects having bad data in
account_username, but it was failing because the try..catch had bad
indentation.  While I fixed that, I also cleaned up the method a bit
and also made it so that it fixes the data in VideoURL if it can.

Replaced videos.tasks._add_amara_description_credit_to_youtube_vurl
with a mock function.  There's no reason that we need to run this task
in the tests.
accountlinker unittest fixes

Made the tests pass, they were failing on my vagrant box and I'm
pretty sure they would fail on the staging server as well.

Made the tests use factory functions instead of fixtures.

Added function in test_factories to create a ThirdPartyAccount
Merge pull request #211 from pculture/i-2587

I 2587