glusterd: Avoid spurious WARNING 'op_ctx modification failed'

This patch fixes by wrapping this whole scenario and skips
op_ctx modification for necessary commands.

Change-Id: I3ecec19caefdc699d9a2dabfb456a89758ae4aa4
BUG: 1066529
Signed-off-by: Harshavardhana <harsha@harshavardhana.net>
Reviewed-on: http://review.gluster.org/8337
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Atin Mukherjee <amukherj@redhat.com>
Reviewed-by: Krishnan Parthasarathi <kparthas@redhat.com>
Tested-by: Krishnan Parthasarathi <kparthas@redhat.com>