CLOUDSTACK-2104: add state change in createVolume back to Allocated if

anything fails

Changes:
createVolume changes the volume state from 'Allocated' to 'Creating',
but has no code to change it back to 'Allocated' if anything goes wrong,
despite there already being a path from 'Creating' to 'Allocated' for
volumes, via the OperationFailed event. Adding this in fixes the issue
and avoids leaving disks in an unusable state.

Testing:
Tested in devcloud-kvm, volume that was larger than primary storage
failed to attack, and went back to 'Allocated' from 'Creating' upon the
failure. I was then able to retry, and delete the disk.

server/src/com/cloud/storage/StorageManagerImpl.java

@@ -837,6 +837,11 @@ public class StorageManagerImpl extends ManagerBase implements StorageManager, C
         }
 
         if (created == null) {
+            try {
+                stateTransitTo(volume, Volume.Event.OperationFailed);
+            } catch (NoTransitionException e) {
+                s_logger.debug("Unable to update volume state: " + e.toString());
+            }
             return null;
         } else {
             volume.setFolder(pool.getPath());