Make OS-FEDERATION core.Driver methods abstract
Make OS-FEDERATION core.Driver methods abstract

Not all methods in contrib.federation.core.Driver are decorated
with @abs.abstractmethod. This patch adds missing decorators.

Change-Id: I93962110134d4b9062a75c228760333403a4f7eb

promptworks/keystone,dstanek/keystone,reeshupatel/demo,jumpstarter-io/keystone,idjaw/keystone,dims/keystone,promptworks/keystone,mahak/keystone,vivekdhayaal/keystone,ilay09/keystone,rushiagr/keystone,maestro-hybrid-cloud/keystone,vivekdhayaal/keystone,himanshu-setia/keystone,ajayaa/keystone,ging/keystone,jonnary/keystone,nuxeh/keystone,cernops/keystone,openstack/keystone,reeshupatel/demo,cernops/keystone,dstanek/keystone,ajayaa/keystone,promptworks/keystone,mahak/keystone,klmitch/keystone,UTSA-ICS/keystone-kerberos,jamielennox/keystone,rushiagr/keystone,nuxeh/keystone,roopali8/keystone,jonnary/keystone,MaheshIBM/keystone,dstanek/keystone,rodrigods/keystone,jamielennox/keystone,MaheshIBM/keystone,dims/keystone,blueboxgroup/keystone,UTSA-ICS/keystone-kerberos,openstack/keystone,jumpstarter-io/keystone,maestro-hybrid-cloud/keystone,blueboxgroup/keystone,rushiagr/keystone,vivekdhayaal/keystone,ging/keystone,rajalokan/keystone,idjaw/keystone,jumpstarter-io/keystone,rajalokan/keystone,rodrigods/keystone,takeshineshiro/keystone,roopali8/keystone,takeshineshiro/keystone,klmitch/keystone,mahak/keystone,ilay09/keystone,himanshu-setia/keystone,openstack/keystone,ilay09/keystone,nuxeh/keystone,rajalokan/keystone,reeshupatel/demo