Deactivate pithos disk space usage tests
Pithos usage tests require special setupsince test accounts should be created and configured properlyin astakos and quotaholder components.
Also, these tests should know the server's version accounting policy.For the time being, pithos server does not return this information....
Eliminate mutable default arguments
Fix pithos purging accounting
Refs: #3442Refs: #1733
Make snf-pithos-tools obsolete
Move the directory under contrib and remove the correspondingentry from `devflow.conf'.