Update keystone conf files for Juno

* Update paste.ini
* Update keystone.conf
  - Add in description comments
  - Add project_ for deprecated ldap tenant_
  - Remove unused user and group _domain_id_attributes
* Update specs as needed

Change-Id: Ifbd5fac220fff7723b3de349ca57cd96a4b6910a
Closes-bug: #1351459