Add keystone_authtoken section into the heat.conf.sample

We support (and need) this section, now that oslo config generator
supports external modules lets add the section into the sample.

Change-Id: I3f7f614906204fa2e5a743c62882d2dcf196640a
Imported Translations from Transifex

Change-Id: Ia2a7f4a7d4a79890b20adeb2d50314c3791727af
Merge "Add keystone_authtoken section into the heat.conf.sample"