Bring initial DiskDir module coverage to 97%.

This is quite ugly. Sorry. We ported a set of test from OpenStack
Swift's test/unit/commont/test_db.py, the testAccountBroker and
testContainerBroker, but because of the divergent nature of the
current attempt UFO (Unified File and Object) implementation, it was
not possible to use the interface calls directly.

Instead, we are using these tests to make sure most of the code paths
are exercised, and to define much of the expected behavior. Further
refactoring, unit tests and functional test work will help us bring
the code base and these tests closer to the originals in upstream
OpenStack Swift (as of Havana).

Change-Id: I095bb03619de6e7e1378b5252913e39b1ea8bf27
Signed-off-by: Peter Portante <peter.portante@redhat.com>
Reviewed-on: http://review.gluster.org/5135
Reviewed-by: Luis Pabon <lpabon@redhat.com>
Tested-by: Luis Pabon <lpabon@redhat.com>