tests: adding missing cleanupNet and refined testQosNetwork.

Some additional cleanupNet were necessary on some tests
which might, on possible failure, make the env dirty.
Added the deletion of network created in the testQosNetwork.

Change-Id: I2fa9619a38acdfcc19f889329d375f868a3e921e
Signed-off-by: Giuseppe Vallarelli <gvallare@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/17941
Reviewed-by: Antoni Segura Puimedon <asegurap@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>