Update documentation for using keystone auth

Cleanup and add clarification to the documentation
for using Keystone auth.

Update to refer to auth_token middleware being
distributed as part of the keystomemiddelware project
rather than keystone.

Include capabilities (/info) in the list of reasons
why delay_auth_decision might need to be set in
auth_token middleware config.

Add description of the project_id:user_id format
for container ACLs and emphasize that ids rather than
names should be used since this patch has now merged:
https://review.openstack.org/#/c/86430

DocImpact
blueprint keystone-v3-support
Change-Id: Idda4a3dcf8240474f1d2d163016ca2d40ec2d589
Merge "Update documentation for using keystone auth"