make volume size parametric in boot_from_volume

Fixes bug #1090007

Change-Id: Ifa13b0b7b62be75805db2730cb7154406f0c1b94
diff --git a/exerciserc b/exerciserc
index 82c74b7..c26ec2c 100644
--- a/exerciserc
+++ b/exerciserc
@@ -26,3 +26,7 @@
 
 # Max time to wait for a euca-delete command to propogate
 export VOLUME_DELETE_TIMEOUT=${SNAPSHOT_DELETE_TIMEOUT:-60}
+
+# The size of the volume we want to boot from; some storage back-ends
+# do not allow a disk resize, so it's important that this can be tuned
+export DEFAULT_VOLUME_SIZE=${DEFAULT_VOLUME_SIZE:-1}