glusterd: Improve debugging experience for glusterd locks

Today, when glusterd's internal locking mechanism fails
with invalid type or when another competing lock is being
held, the log message doesn't provide enough information
directly as to which command saw this (first). Following
is a snippet of how a failure would look in the log file.
This would greatly assist in debugging.

[2014-09-03 04:57:58.549418] E
[glusterd-locks.c:520:glusterd_mgmt_v3_lock]
(-->/usr/local/lib/glusterfs/3.7dev/xlator/mgmt/glusterd.so(__glusterd_handle_create_volume+0x801)
[0x7f30b071e651]
(-->/usr/local/lib/glusterfs/3.7dev/xlator/mgmt/glusterd.so(glusterd_op_begin_synctask+0x2c)
[0x7f30b072e19c]
(-->/usr/local/lib/glusterfs/3.7dev/xlator/mgmt/glusterd.so(gd_sync_task_begin+0x55d)
[0x7f30b072de6d]))) 0-management: Invalid entity. Cannot perform locking
operation on vol types

Change-Id: I0595f49d60e620e8b065f3506bdb147ccee383a7
BUG: 1145093
Signed-off-by: Krishnan Parthasarathi <kparthas@redhat.com>
Reviewed-on: http://review.gluster.org/8842
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>