net tests: add a minimal test for getVdsStats

This patch verifies that the vlan devices added by
testSetupNetworksAddBondWithManyVlans are reported by getVdsStats.

Change-Id: I6d762b7b7b9f0592702f1f2a64e1adf0c16c8ad7
Signed-off-by: Dan Kenigsberg <danken@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/30552
Reviewed-by: Antoni Segura Puimedon <asegurap@redhat.com>