make volume size parametric in boot_from_volume

Fixes bug #1090007

Change-Id: Ifa13b0b7b62be75805db2730cb7154406f0c1b94
diff --git a/exercises/boot_from_volume.sh b/exercises/boot_from_volume.sh
index 5ebdecc..5ada237 100755
--- a/exercises/boot_from_volume.sh
+++ b/exercises/boot_from_volume.sh
@@ -117,7 +117,7 @@
 fi
 
 # Create the bootable volume
-cinder create --display_name=$VOL_NAME --image-id $IMAGE 1
+cinder create --display_name=$VOL_NAME --image-id $IMAGE $DEFAULT_VOLUME_SIZE
 
 # Wait for volume to activate
 if ! timeout $ACTIVE_TIMEOUT sh -c "while ! cinder list | grep $VOL_NAME | grep available; do sleep 1; done"; then