SCST tokens are now stored in the 'tokens' table.
This unifies old token handling and new subclient-specific tokens.
Also ensures the BlenderID expiry of the token is taken into account.
Removes use of httpretty, in favour of responses.
Also converted test_auth.py to use the new AbstractPillarTest class.
This class ensures that we test against the testing database, which
is dropped at every setUp()/tearDown().
