tests: Fix unit tests after auth was merged

V2->V3:
 - Fixed test_mockmodel.py failures

V1->V2:
 - Fixed test_exception.py failures

The Authentication series broke the test suite badly.  This patch adds
HTTP Basic Auth headers to client requests so they can be authenticated
by the server.  The PAM authentication is replaced by a fake function
which checks an internal dictionary of user/password combinations.

One test: test_404 requires us to use the /login REST API to establish a
session.

Signed-off-by: Adam Litke <agl@linux.vnet.ibm.com>
tests: Disable auth debug

The module level debug function in auth.py causes a lot of log noise.
Turn off debugging output by default.

Signed-off-by: Adam Litke <agl@linux.vnet.ibm.com>