Update tempest hacking regarding unit tests

This commit just updates some of the hacking documentation around unit
tests. It also adds a new hacking rule to ensure that setUpClass isn't
used for the unit tests.

Partially implements bp unit-tests

Change-Id: Ie8b1c9f1312a467265d53bc28ee905fa1b5fbb53
Merge "Update tempest hacking regarding unit tests"