Enumerate available options in IPA installer

Fix adds enumerated list of available options in IPA server
installer and IPA CA installer help options

Fixes https://fedorahosted.org/freeipa/ticket/5435

Signed-off-by: Abhijeet Kasurde <akasurde@redhat.com>
Reviewed-By: Jan Cholasta <jcholast@redhat.com>

ipapython/install/cli.py

@@ -179,6 +179,8 @@ class ConfigureTool(admintool.AdminTool):
             elif issubclass(knob_scalar_type, enum.Enum):
                 kwargs['type'] = 'choice'
                 kwargs['choices'] = [i.value for i in knob_scalar_type]
+                kwargs['metavar'] = "{{{0}}}".format(
+                                                ",".join(kwargs['choices']))
             else:
                 kwargs['nargs'] = 1
                 kwargs['callback_args'] = (knob_scalar_type,)