Enable third party auth in LMS acceptance tests

Now that third party auth is enabled in prod, we should also enable it in the acceptance tests.

* Update LMS settings to enable Google and Facebook social auth.
* Update test database caches so they include social auth tables.

The settings use dummy data, so we won't be able to write tests that specifically exercise this feature.  However, simply enabling social auth makes changes to the registration, login, and dashboard pages, which our existing tests will hit.

@flowerhack @benpatterson please review.