Debug/io-stats: Enable INFO level in syslog

Previously we had only ERROR, WARNING and CRITICAL
levels allowed in syslog. Adding INFO level as per
user request.

Change-Id: I3276d62d12ebf4be68edf5e5b26341dc2bb4f47b
BUG: 887924
Signed-off-by: Raghavendra Talur <rtalur@redhat.com>
Reviewed-on: http://review.gluster.org/4499
Reviewed-by: Vijay Bellur <vbellur@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>