Add cache=swift.cache for authtoken example.

- Things swill go badly with swift if we leave the default to authtoken
  to use its own memcache cache connection based python-memcache c based
  binding.

Change-Id: I293b875acdcb06e5a7a0cfa9a9bb5d7678675da0
Merge "Add cache=swift.cache for authtoken example."