Print help on help command

Change it so that 'cliffdemo help' prints the full help, not the
help for the help command.  'cliffdemo help help' can be used to
print the help for the help command.  Running 'cliffdemo help'
will be similar to running 'cliffdemo --help'.

Change-Id: I1b3e5448b2cf357ae65ca86e1131165aff023c39

cliff/help.py

@@ -78,6 +78,7 @@ class HelpCommand(Command):
                          )
             cmd_parser = cmd.get_parser(full_name)
         else:
-            cmd_parser = self.get_parser(' '.join([self.app.NAME, 'help']))
+            action = HelpAction(None, None, default=self.app)
+            action(self.app.parser, self.app.parser, None, None)
         cmd_parser.print_help(self.app.stdout)
         return 0

cliff/tests/test_help.py

@@ -90,7 +90,9 @@ def test_show_help_for_help():
     except SystemExit:
         pass
     help_text = stdout.getvalue()
-    assert 'usage: test help [-h]' in help_text
+    assert 'usage: nosetests [--version]' in help_text
+    assert 'optional arguments:\n  --version' in help_text
+    assert 'one            \n  three word command  \n' in help_text
 
 
 def test_list_deprecated_commands():