Correct docstrings for federation driver interface
Correct docstrings for federation driver interface

A number of the federation driver signature docstings were
missing descriptions of paramaters and/or return values. This
patch adds the missing docstring information.

Change-Id: I59bd800385eb40f1f59c191f0ae8e128eef12e0e

mahak/keystone,rajalokan/keystone,openstack/keystone,mahak/keystone,dims/keystone,cernops/keystone,himanshu-setia/keystone,mahak/keystone,klmitch/keystone,cernops/keystone,dims/keystone,ilay09/keystone,rajalokan/keystone,ilay09/keystone,openstack/keystone,rajalokan/keystone,ilay09/keystone,himanshu-setia/keystone,openstack/keystone,klmitch/keystone