Turn auth_token plugin config blog post into docs

[Dolph Mathews]

The contents of this blog post:

  http://www.jamielennox.net/blog/2015/02/17/loading-authentication-plugins/

Should be on:

  http://docs.openstack.org/developer/keystonemiddleware/

[Anne Gentle (annegentle)]

Does there need to be a separate developer site for keystone middleware? Seems like people are having trouble finding the info and I'm trying to get to root causes. Could be due to a split, could be due to a new site not having search engine power yet. I'd like for something as important to operators and users as these middleware decisions to have better findability, how can you help?

[Matt Kassawara (ionosphere80)]

Nobody updated that documentation for the identity_uri option circa Icehouse either.

[Ian Cordasco (icordasc)]

This would have been helpful to have documented in an easily discoverable place

[Steve Martinelli (stevemar)]

i marked this as a dupe for a general overhaul of our config options, and included a reference to jamie's post in the dupe bug