Display UUIDs and names in gnt-instance info

Modify gnt-instance client to display the UUID and name
fields of instances disks and NICs.

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