Load admin site for Unit Tests, add form tests

Review Request #10339 — Created Nov. 29, 2018 and submitted — Latest diff uploaded

Information

Review Board
master
58f3da5...

Reviewers

The admin site models and URLs were unable to be accessed during Unit Tests.
This meant that if a test attempted to access an admin model page, the
page would respond with a 404 error.

Adding django.contrib.admin.autodiscover() during initial test setup
loads all the admin UI models, so tests have access to admin URLS.

DefaultReviewer form tests, WebhookTargetAdmin form tests, and OauthAdmin
form tests were all added as well, to check that forms function as
expected.

Running ./tests/runtests.py returns no errors. The form tests added
pass.