glusterd: do dict unref after sending reply to cli

This patch channelizes dict unrefs of dictionaries created from the cli
req during volume ops to one common function - glusterd_to_cli() - which
is guaranteed to be called irrespective of whether the command succeeds
or fails.

This patch also removes extra unrefs at a few places.

Change-Id: Ic8ba7166387b5dfd1f5ae860539e1b7093a94662
BUG: 861044
Signed-off-by: Krutika Dhananjay <kdhananj@redhat.com>
Reviewed-on: http://review.gluster.org/4003
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Amar Tumballi <amarts@redhat.com>
Reviewed-by: Anand Avati <avati@redhat.com>