geo-rep/glusterd: API to check active geo-rep session for the volume

Requirement:
Snapshot needs an API to fail the CLI if any geo-rep session is active
for that volume.

Solution:
A function "gd_vol_is_geo_rep_active" is provided to check if any
geo-rep session is active for that volume. An in memory dict called
'gsync_running_slaves' is maintained in 'volinfo' structure to keep
track of active geo-rep session for the volume. The key
'slavenode::slavevol' with value 'running' is added whenever geo-rep
is started/resumed into the dict and the same is removed if
stopped/paused. So the 'count' in dict is used to decide whether the
geo-rep is active or not for that volume.

Also added "this->name" in gf_log in routines which this patch is
touched.

Change-Id: I2b5de7dd686541c6b89c0fd0f7a4dbc92eecfac5
BUG: 1129008
Signed-off-by: Kotresh HR <khiremat@redhat.com>
Reviewed-on: http://review.gluster.org/8459
Reviewed-by: Krishnan Parthasarathi <kparthas@redhat.com>
Tested-by: Krishnan Parthasarathi <kparthas@redhat.com>