MigrationsTestCase is intentionally omitted from this, since migrations
tests are different in their nature and so whatever setUp()
ZulipTestCase may do in the future, MigrationsTestCase may not
necessarily want to replicate.
Apparently, zoom's API will (sometimes?) return a 201 (not 200)
created in response to the API request to create a call. We fix this
by using the proper requests check for whether or not the request
failed.
Mateusz Mandera
Tim Abbott
Marco Burstein