Use correct class path for token persistence backend

Keystone has moved over to using a new location for the token
persistence backends (drivers). The old values will continue to
work, but this will limit the deprecation warnings for an out
of the box devstack install.

Change-Id: I7c437788c8aee0106fa7f3c37617fbd1220291ef
bp: non-persistent-tokens
Merge "Use correct class path for token persistence backend"