tests: setupNetworks convertVlanNetBridgeness, Mtus

Added a couple of functional tests:

* testSetupNetworksConvertVlanNetBridgeness
  covering behavior of converstion of a network
  from bridged to bridgeless and viceversa.

* testSetupNetworksMtus covering behaviour of
  setupNetworks when used with different mtus.

Change-Id: Ib8723b066228729807f7ab46c9fabad3ebff128b
Signed-off-by: Giuseppe Vallarelli <gvallare@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/17866
Reviewed-by: Dan Kenigsberg <danken@redhat.com>
Tested-by: Dan Kenigsberg <danken@redhat.com>