use expected_length parameter to assert expected length
use expected_length parameter to assert expected length

assertValidRoleAssignmentListResponse method provides expected_length
parameter to assert expected length of list response. However, we
do not use it.

Change-Id: Ifc9ff3f13809ef939d2154d1ddd8648735efb613

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