Stop using tearDown.

TestCase.tearDown doesn't get called if setUp fails, it should never
be used.

Change-Id: Ib960c3f9610d8d8a0624e0c0709afa819e1858ad
Stop resetting logging on every call to __main__.

__main__ is called directly during tests, but was resetting the
logging environment within it, which prevented tests from capturing
the log events.

Change-Id: If710e11091723144c97c88aab4aa5e6126844d2b