Add exception text to exit message (#530)

If `clientsecrets.InvalidClientSecretsError` is raised with additional
text and a predefined failure message is given, include exception text
in the exit message.

oauth2client/client.py

@@ -2210,8 +2210,10 @@ def flow_from_clientsecrets(filename, scope, redirect_uri=None,
                 client_info['client_id'], client_info['client_secret'],
                 scope, **constructor_kwargs)
 
-    except clientsecrets.InvalidClientSecretsError:
-        if message:
+    except clientsecrets.InvalidClientSecretsError as e:
+        if message is not None:
+            if e.args:
+                message = 'The client secrets were invalid: \n{0}\n{1}'.format(e, message)
             sys.exit(message)
         else:
             raise

tests/test_client.py

@@ -2150,6 +2150,20 @@ class FlowFromCachedClientsecrets(unittest2.TestCase):
         sys_exit.assert_called_once_with(message)
         loadfile_mock.assert_called_once_with(filename, cache=cache)
 
+    @mock.patch('oauth2client.clientsecrets.loadfile',
+                side_effect=InvalidClientSecretsError('foobar'))
+    @mock.patch('sys.exit')
+    def test_flow_from_clientsecrets_invalid_w_msg_and_text(self, sys_exit,
+                                                            loadfile_mock):
+        filename = object()
+        cache = object()
+        message = 'hi mom'
+        expected = 'The client secrets were invalid: \n{0}\n{1}'.format('foobar', 'hi mom')
+
+        flow_from_clientsecrets(filename, None, cache=cache, message=message)
+        sys_exit.assert_called_once_with(expected)
+        loadfile_mock.assert_called_once_with(filename, cache=cache)
+
     @mock.patch('oauth2client.clientsecrets.loadfile')
     def test_flow_from_clientsecrets_unknown_flow(self, loadfile_mock):
         client_type = 'UNKNOWN'