Added a sleep before mounting. Added an error message on mount error.

start_or_update.sh

@@ -8,7 +8,9 @@ do
     then
          VOLUME_ID=$(/home/yohan/env_py3/bin/openstack volume show ${VOLUME} -c id --format value)
          test -e /dev/disk/by-id/*${VOLUME_ID:0:20} || nova volume-attach $INSTANCE $VOLUME_ID auto
+         sleep 3
          sudo mount /dev/disk/by-id/*${VOLUME_ID:0:20} /mnt/volumes/${VOLUME}
+         mountpoint -q /mnt/volumes/${VOLUME} || { echo "ERROR: could not mount /mnt/volumes/${VOLUME}, exiting."; exit 1; }
     fi
 done