who-wrote-glusterfs: use the set $GITDM_REPO variable

Change-Id: Ic119f83fff3930e164f3c81df1c9b60d5eb2d99f
BUG: 1131272
Signed-off-by: Patrick Uiterwijk <puiterwijk@redhat.com>
Reviewed-on: http://review.gluster.org/8495
Reviewed-by: Humble Devassy Chirammal <humble.devassy@gmail.com>
Reviewed-by: Niels de Vos <ndevos@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>