glusterfsd: TRACE is a valid log level too

Change-Id: Ia17513817f8f6d7a4a8732fc0cfee21f16a75fac
Signed-off-by: Lubomir Rintel <lubo.rintel@gooddata.com>
Reviewed-on: http://review.gluster.org/5401
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>