Stronger assertion for test_user_extra_attribute_mapping
Stronger assertion for test_user_extra_attribute_mapping

The assertion was checking if the value was in the list, but it's
actually the only element in the list.

Change-Id: I8666736ec0eec5a859e646a3e0328a8e6baccde7

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