geo-rep / gsyncd: Separate log file directory for Mountbroker sessions

... so that a mountbroker session which is initiated b/w master
and slave does not use the same log file if it's started after
a normal geo-rep session b/w master and slave. This results in
EPERM as the log file is owned by root and the geo-rep slave
process (now running as a non privileged user) does not have
access to it.

Also, having separate log file directory for mountbroker sessions
looks clean.

NOTE: geo-rep's client mount log file location remains unchanged.

Change-Id: Ic7a732e250aee5393b9c3f6ebf6dfe2c310b7fe4
BUG: 893960
Signed-off-by: Venky Shankar <vshankar@redhat.com>
Reviewed-on: http://review.gluster.org/4407
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Anand Avati <avati@redhat.com>