rpc: change dict key for fqdn

changed the key from "client.fqdn", which could be wrongly
construed as belonging to protocol/client, to "fqdn".

Change-Id: Ib5f4a875a00b99cd903a29da19bafeb70baaab4e
BUG: 906119
Signed-off-by: Rajesh Amaravathi <rajesh@redhat.com>
Reviewed-on: http://review.gluster.org/4536
Reviewed-by: Niels de Vos <ndevos@redhat.com>
Reviewed-by: Kaleb KEITHLEY <kkeithle@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>