export DIB_DEBUG_TRACE

Make the disk-image-create execution verbose, so it is easier to spot
failures in scripts.

(Theoretically, -x can be passed to disk-image-create to get the same
result, but diskimage-create.sh does not support that, so use
DIB_DEBUG_TRACE which will work regardless.)

Change-Id: I5b13af7601f1ac0e21c4281d94472595aa2439c3

slave-scripts/dib.sh

@@ -28,6 +28,9 @@ cdh_image=$HOST-${image_type}-cdh-${ZUUL_CHANGE}
 # Clone Sahara
 git clone https://review.openstack.org/openstack/sahara $SAHARA_PATH
 
+# make verbose the scripts execution of disk-image-create
+export DIB_DEBUG_TRACE=1
+
 case $job_type in
     vanilla*)
        if [ "${image_type}" == 'centos' ]; then