rpc,glusterd: Use rpc_clnt notifyfn to cleanup mydata

rpc:
- On a RPC_TRANSPORT_CLEANUP event, rpc_clnt_notify calls the registered
  notifyfn with a RPC_CLNT_DESTROY event. The notifyfn should properly
  cleanup the saved mydata on this event.
- Break the reconnect chain when an rpc client is disabled. This will
  prevent new disconnect events which can lead to crashes.

glusterd:
- Added support for RPC_CLNT_DESTROY in glusterd_brick_rpc_notify
- Use a common glusterd_rpc_clnt_unref() function throught glusterd in
  place of rpc_clnt_unref(). This function correctly gives up the
  big-lock before performing the unref.

Change-Id: I93230441c5089039643fc9f5632477ef1b695348
BUG: 962619
Signed-off-by: Kaushal M <kaushal@redhat.com>
Reviewed-on: http://review.gluster.org/5512
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Krishnan Parthasarathi <kparthas@redhat.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>