Add CLI parsing tests

These test that command lines are parsed to correct Command arguments.
Includes some tests for interactive prompts.

To make this possible cli.run is broken up into several pieces.

ipalib/__init__.py

@@ -916,5 +916,8 @@ def create_api(mode='dummy'):
 api = create_api(mode=None)
 
 if os.environ.get('IPA_UNIT_TEST_MODE', None) == 'cli_test':
+    from cli import cli_plugins
+    for klass in cli_plugins:
+        api.register(klass)
     api.bootstrap(context='cli', in_server=False, in_tree=True)
     api.finalize()