cluster/dht: print hash function munging logs in DEBUG mode

Change-Id: Ia2e6bce80710d103da9d78afdb389ea162b00686
BUG: 912564
Signed-off-by: Anand Avati <avati@redhat.com>
Reviewed-on: http://review.gluster.org/4590
Reviewed-by: Jeff Darcy <jdarcy@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>