glusterd: Validating invalid log-level under geo-rep config options.

Change-Id: I8ff6b48ef41fd6e9ea68c42dfb9878f8a08ed627
BUG: 1010874
Signed-off-by: Ajeet Jha <ajha@redhat.com>
Reviewed-on: http://review.gluster.org/5989
Reviewed-by: Avra Sengupta <asengupt@redhat.com>
Reviewed-by: Amar Tumballi <amarts@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Venky Shankar <vshankar@redhat.com>