Improve neutron-client error message output

In case a user provides incorrect input, the NOVA CLIs provide
information regarding usage of the NOVA help CLI. This is useful
for new users. Similar information has been updated in the neutron
CLIs as well.

Change-Id: I1be2ba5a2c937b58900221a9ec7625c461ac17d9
Closes-Bug: #1495742

neutronclient/shell.py

@@ -818,6 +818,10 @@ class NeutronShell(app.App):
                          )
             cmd_parser = cmd.get_parser(full_name)
             return run_command(cmd, cmd_parser, sub_argv)
+        except SystemExit:
+            print(_("Try 'neutron help %s' for more information.") %
+                  cmd_name, file=sys.stderr)
+            raise
         except Exception as e:
             if self.options.verbose_level >= self.DEBUG_LEVEL:
                 self.log.exception("%s", e)

neutronclient/tests/unit/test_shell.py

@@ -59,7 +59,9 @@ class ShellTest(testtools.TestCase):
                 fixtures.EnvironmentVariable(
                     var, self.FAKE_ENV[var]))
 
-    def shell(self, argstr, check=False):
+    def shell(self, argstr, check=False, expected_val=0):
+        # expected_val is the expected return value after executing
+        # the command in NeutronShell
         orig = (sys.stdout, sys.stderr)
         clean_env = {}
         _old_env, os.environ = os.environ, clean_env.copy()
@@ -70,7 +72,7 @@ class ShellTest(testtools.TestCase):
             _shell.run(argstr.split())
         except SystemExit:
             exc_type, exc_value, exc_traceback = sys.exc_info()
-            self.assertEqual(0, exc_value.code)
+            self.assertEqual(expected_val, exc_value.code)
         finally:
             stdout = sys.stdout.getvalue()
             stderr = sys.stderr.getvalue()
@@ -211,3 +213,15 @@ class ShellTest(testtools.TestCase):
 
         namespace = parser.parse_args([])
         self.assertEqual(50, namespace.http_timeout)
+
+    def test_run_incomplete_command(self):
+        self.useFixture(fixtures.FakeLogger(level=logging.DEBUG))
+        cmd = (
+            '--os-username test --os-password test --os-project-id test '
+            '--os-auth-strategy keystone --os-auth-url '
+            '%s port-create' %
+            DEFAULT_AUTH_URL)
+        stdout, stderr = self.shell(cmd, check=True, expected_val=2)
+        search_str = "Try 'neutron help port-create' for more information"
+        self.assertTrue(any(search_str in string for string
+                            in stderr.split('\n')))