cinder: Increase VOLUME_BACKING_FILE_SIZE

As reported in bug #1920136 the tempest-integrated-compute job has
started to see insufficient free virtual space errors being reported by
c-sch and c-vol when creating volumes. This change simply increases the
default size of the underlying LVM PV used to host these volumes within
the default LVM/iSCSI c-vol backend deployed by devstack.

Change-Id: I965d4a485215ac482403f1e83609452550dfd860
Closes-Bug: #1920136

Author: lyarwood

stackrc

@@ -758,8 +758,8 @@ for image_url in ${IMAGE_URLS//,/ }; do
     fi
 done
 
-# 24Gb default volume backing file size
-VOLUME_BACKING_FILE_SIZE=${VOLUME_BACKING_FILE_SIZE:-24G}
+# 30Gb default volume backing file size
+VOLUME_BACKING_FILE_SIZE=${VOLUME_BACKING_FILE_SIZE:-30G}
 
 # Prefixes for volume and instance names
 VOLUME_NAME_PREFIX=${VOLUME_NAME_PREFIX:-volume-}