[FIX] rpc: correctly handle xmlrpclib.Fault

The error string was always missing, despite being provided.

Backport in #22276 courtesy of Yenthe V.G

Fixes #13111
Closes #21741
Closes #22276

openerp/service/wsgi_server.py

@@ -65,7 +65,7 @@ def xmlrpc_return(start_response, service, method, params, string_faultcode=Fals
 
 def xmlrpc_handle_exception_int(e):
     if isinstance(e, openerp.exceptions.UserError):
-        fault = xmlrpclib.Fault(RPC_FAULT_CODE_WARNING, openerp.tools.ustr(e.value))
+        fault = xmlrpclib.Fault(RPC_FAULT_CODE_WARNING, openerp.tools.ustr(e.name))
         response = xmlrpclib.dumps(fault, allow_none=False, encoding=None)
     elif isinstance(e, openerp.exceptions.RedirectWarning):
         fault = xmlrpclib.Fault(RPC_FAULT_CODE_WARNING, str(e))