Use abstract base class for auth handler
Use abstract base class for auth handler

Use the abc module for managing abstract base classes in the driver
layer.

bp abstract-base-class-drivers

Change-Id: I302a9bf0ac3aea2a2f687e0ceda7e107c0c11539

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