Login operation though horizon always failed when keystone use LDAP backends.

Issue

• Login operation though horizon always failed when keystone use LDAP backends.
• httpd for keystone generates following error.

File "/usr/lib/python3.6/site-packages/keystone/assignment/core.py", line 232, in list_dom
  user_id=user_id, effective=True)                                                        
File "/usr/lib/python3.6/site-packages/keystone/common/manager.py", line 116, in wrapped  
  __ret_val = __f(*args, **kwargs)                                                        
File "/usr/lib/python3.6/site-packages/keystone/assignment/core.py", line 998, in list_rol
  strip_domain_roles)                                                                     
File "/usr/lib/python3.6/site-packages/keystone/assignment/core.py", line 851, in _list_ef
  group_ids = self._get_group_ids_for_user_id(user_id)                                    
File "/usr/lib/python3.6/site-packages/keystone/assignment/core.py", line 88, in _get_grou
  x in PROVIDERS.identity_api.list_groups_for_user(user_id)]                              
File "/usr/lib/python3.6/site-packages/keystone/common/manager.py", line 116, in wrapped  
  __ret_val = __f(*args, **kwargs)                                                        
File "/usr/lib/python3.6/site-packages/keystone/identity/core.py", line 414, in wrapper   
  return f(self, *args, **kwargs)                                                         
File "/usr/lib/python3.6/site-packages/keystone/identity/core.py", line 424, in wrapper   
  return f(self, *args, **kwargs)                                                         
File "/usr/lib/python3.6/site-packages/keystone/identity/core.py", line 1312, in list_grou
  ref_list, domain_id, driver, mapping.EntityType.GROUP)                                  
File "/usr/lib/python3.6/site-packages/keystone/identity/core.py", line 603, in _set_domai
  ref, domain_id, driver, entity_type, conf)                                              
File "/usr/lib/python3.6/site-packages/keystone/identity/core.py", line 693, in _set_domai
  self._insert_new_public_id(local_entity, ref, driver)                                   
File "/usr/lib/python3.6/site-packages/keystone/identity/core.py", line 619, in _insert_ne
  local_entity, public_id)                                                                
File "/usr/lib/python3.6/site-packages/keystone/common/manager.py", line 116, in wrapped  
  __ret_val = __f(*args, **kwargs)                                                        
File "/usr/lib/python3.6/site-packages/keystone/identity/core.py", line 1465, in create_id
  public_id = self.driver.create_id_mapping(local_entity, public_id)                      
File "/usr/lib/python3.6/site-packages/keystone/identity/mapping_backends/sql.py", line 77
  entity)                                                                                 
File "/usr/lib/python3.6/site-packages/keystone/identity/id_generators/sha256.py", line 25
  m.update(mapping[key].encode('utf-8'))