Add unit tests for unified network persistence

Change-Id: I0221f2e0313a80d0ed5ce2d5406dc45f08ab26dd
Signed-off-by: Assaf Muller <amuller@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/21269
Reviewed-by: Dan Kenigsberg <danken@redhat.com>