SouthboundIT: make the tests uniform

All the CRUD tests should be similar; fix all the NPE handling and
adjust the tests so they are all used. This is a precursor to merging
all the tests using helper classes.

Change-Id: Ie616bed00304ddc780b85f0bd0d0f550bb4645f2
Signed-off-by: Stephen Kitt <skitt@redhat.com>