Support Storage Policy - Rev 7

* Rename references of '/mnt/gluster-object' to '/mnt/swiftonfile'.
* Rename swiftonfile SP name from 'sof' to 'swiftonfile'.
* Retain reseller_prefix in account dir created. This is to comply
  with Swift's behavior.
* Cleanup mountpoint after running swiftonfile specific tests.

Signed-off-by: Prashanth Pai <ppai@redhat.com>