glusterd: Give up big lock before performing any RPC

Change-Id: Ib0a772dc1cb9afc8adccd8f7092f480d2b525ea0
BUG: 960580
Signed-off-by: Krishnan Parthasarathi <kparthas@redhat.com>
Reviewed-on: http://review.gluster.org/4964
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Anand Avati <avati@redhat.com>