Modify query LUs to supoprt nic.network as uuid

Make _InstanceQuery gather all network info related to instance's
NICs and in case of NETQ_INST in _NetworkQuery get all network
uuids directly from nic.network

Signed-off-by: Dimitris Aragiorgis <dimara@grnet.gr>
Reviewed-by: Helga Velroyen <helgav@google.com>