RCv3 positive integration tests

Closes #840.
> tearDown removes per-test resources. tearDownClass removes resources shared by all tests.

The important distinction is that the `tearDownClass` removes resources shared by all the tests, <b> after </b> all the tests in that class have executed. So using `tearDown` will still help. 

However, I understand that Otter responds with a 204 and then deletes all the servers and nodes on the group, and that we will need for a way to not just poll for a successful group deletion but also ensure all the resources were successfully deleted. Maybe use `empty_scaling_group` from the fixtures and poll for the group to have 0 active servers(assuming the sever is deleted after it has been removed from the lb pool) as part of the tearDown to fix #855 ?