Subclasses of TestCase don't need to reset conf

Subclasses of TestCase were unnecessarily resetting the config on
cleanup. This is unnecessary because TestCase resets the config
already.

This takes care of some TODOs in the code.

Change-Id: I4350efb03a40616e6a9e7fb6ee7cc507f4709f00
Fix sample config external default doc

The sample config file documented the incorrect default for the
[auth].external value as defined in keystone.common.config.

Change-Id: I6f9454f35eaade5fa35738a9ba3f74a388bf5099
Document running with pdb

There was no documentation in "Developing with Keystone" that
makes it obvious that you can use "tox -e debug" to run with pdb
breakpoints.

Change-Id: I82cc827d076a4d95ab6a2f903ceb0cde34005bc3
Merge "Document running with pdb"
Merge "Fix sample config external default doc"
Merge "Subclasses of TestCase don't need to reset conf"