Let's use sphinx extensions to generate the config options instead of
updating them manually.
The following options will no longer appear since we use auth plugins
now:
auth_admin_prefix
auth_url
auth_host
auth_port
auth_protocol
identity_uri
admin_token
admin_user
admin_password
admin_tenant_name
Change-Id: I0a6eac26f93bfb1c2cbba17a98629108915f78c6