Ie6a6003d667c8c6045439ca3d35f0f121097bddc removed the inclusion of
::mistral::keystone::authtoken in the ::mistral class. This change adds
it to the api configuration which matches what we have for other
modules. Additionally this change add auth_strategy to the api class to
allow users to be able to disable it if they don't want to configuration
keystone.
Change-Id: I68037d0a1f8f43ca40ef6faff119c3fb4b535a90
Closes-Bug: #1777541
b8612ad8d3