log: add comments to rsyslog gluster configuration file

Comments are added to rsyslog gluster configuration files to give
clear meanings and example email alerting.

Change-Id: I23577dc3b39bca89696c46ab6252dc5673d0803f
BUG: 928648
Signed-off-by: Bala.FA <barumuga@redhat.com>
Reviewed-on: http://review.gluster.org/5621
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>