fix assertTableColumns
fix assertTableColumns

assertTableColumns method is used to asserts that the table contains
the expected set of columns. There is a assert in assertTableColumns:
self.assertEqual(expected_cols.sort(), actual_cols.sort()).
However, the return of List.sort is None. So, this assert always
passes.

Change-Id: I4b5e48044cb466b1660484043b475ac6e2d9b35e
Closes-Bug: #1421092

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