Fix keystone.tests.unit.test_backend_ldap.LDAPIdentity
Fix keystone.tests.unit.test_backend_ldap.LDAPIdentity

* Config option [ldap]/alias_dereferencing only allows value in
  [never, searching, always, finding, default], oslo.config will
  ensure that, so don't need test the case.

* Config option [ldap]/query_scope only allows value in [one, sub],
  oslo.config will ensure that, so don't need test the case.

Partial-Bug: #1686921

Change-Id: Ie262acd0386318ff5f818f8688bdbb40f4939360

rajalokan/keystone,rajalokan/keystone,openstack/keystone,mahak/keystone,rajalokan/keystone,mahak/keystone,openstack/keystone,openstack/keystone,mahak/keystone