why we delete prmary storage pool every time when stopping vm?

[Edison Su]

Hi Mike,
   I looked at your commit: 858ce766659101eb731c83c806892dd5d9baa976, seems it 
will  try to delete primary storage every time when stopping a VM ,which maybe 
the root cause a kvm blocker bug: CLOUDSTACK-5432, KVM guest vms are crashed 
during the automation test. From the agent log, I find a lot of "umount " 
primary storage error.
  In 4.2, we never do that kind of operation. Do you know why we add it in 4.3? 
I am referring to the code in :

disconnectPhysicalDiskByPath in LibvirtStorageAdaptor