Heat - revise keystone/trusts config to avoid deprecated options
Heat - revise keystone/trusts config to avoid deprecated options

There are some inter-related changes required to avoid using legacy
fallback/deprecated paths in heat, which result in warnings in the
log, e.g because we fall-back to reusing keystone auth_token
configuration instead of heat specific sections.

To fix this:
- Don't explicitly set deferred_auth_method=trusts, as this is now
  the default (since kilo)
- Create a new "trustee" section containing configuration used for
  the password auth-plugin associated with deferred authentication
  via trusts (support for this was added during liberty to enable
  us to stop incorrectly using the keystone auth_token config)
- Create a "clients_keystone" section to avoid falling back to the
  legacy behavior of stealing the uri from auth_token.

This also means we can remove the FIXME and auth_token auth_uri
mentioned by jamielennox.

Change-Id: Ie34332a7aec3b9b271df0759dd6ab66b45302832
Related-Bug: #1300246

bswartz/devstack,dtroyer/devstack,nawawi/openstack,group-policy/devstack,noironetworks/devstack,dtroyer/devstack,mssumanth/devstack,mssumanth/devstack,bigswitch/devstack,dirkmueller/devstack,noironetworks/devstack,avvocatodemarchis/devstack,group-policy/devstack,samgoon/devstack,Mahito/devstack,bigswitch/devstack,richliu/devstack,nawawi/openstack,richliu/devstack,openstack-dev/devstack,avvocatodemarchis/devstack,bswartz/devstack,Mahito/devstack,dirkmueller/devstack,samgoon/devstack,openstack-dev/devstack