glusterd: logging improvement in txn_opinfo getter/setter function

There is a code path (__glusterd_handle_stage_op) where glusterd_get_txn_opinfo
may fail to get a valid transaction id if there is no volume name provided in
the command, however if this function fails to get a txn id in op state machine
then its a serious issue and op-sm is impacted. From debugability aspect gf_log
() can never give the consumer of this function, so logging these failures with
gf_log_calling_fn is must here.

Change-Id: I4937a9fb20cc6a747fd30dcd9fd4936398d0602a
BUG: 1168809
Signed-off-by: Atin Mukherjee <amukherj@redhat.com>
Reviewed-on: http://review.gluster.org/9207
Reviewed-by: Avra Sengupta <asengupt@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Krishnan Parthasarathi <kparthas@redhat.com>
Tested-by: Krishnan Parthasarathi <kparthas@redhat.com>