[all] oslotest removing mock as a dependency

Hi all, In keeping with the move from the third-party mock library to the built-in unittest.mock module, oslotest is removing mock as a dependency (again). We tried this at the end of the last cycle, but it turned out a number of projects were relying on oslotest to pull in mock for them so in order to not hold up the release we reverted the change. We've un-reverted it and the release request is now merged, so if you were previously relying on oslotest to install mock in your tests you will now need to do one of the following: 1) Migrate to unittest.mock (preferred) or 2) Explicitly depend on mock in your test-requirements.txt. If you have any questions about this, let us know. Thanks. -Ben