log: send current gf_log to syslog conditionally

When compile time option GF_USE_SYSLOG is enabled (which is default),
generated logs are sent to syslog with error code ERR_DEV.

User can opt to use traditional log at run time by creating
/var/log/glusterd/logger.conf file and restarting respective gluster
services.

Change-Id: I9837d0f99da1afc2189d7ecd214c4293ec53715a
BUG: 928648
Signed-off-by: Bala.FA <barumuga@redhat.com>
Reviewed-on: http://review.gluster.org/5002
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>