Add python-keystoneclient-federation to the Identity program

Similar to the python-keystoneclient-kerberos auth plugin, the federation
auth plugin for keystoneclient requires external dependencies that should
not be required for all installations of keystoneclient. Therefore this
plugin has been added as a separate repository and package (on pypi).

Change-Id: I8e6ba4d8ef41dce84748574956fba485ec79919b
Merge "Add python-keystoneclient-federation to the Identity program"