install: use standard Python classes to declare knob types

Use type(None) rather than bool to define knobs which are represented as
command line flags. This allows declaring both "--option" and
"--option={0,1}"-style command line options.

Use enum.Enum subclasses instead of set literals to declare enumerations.

Use typing.List[T] instead of (list, T) to declare lists. (Note that a
minimal reimplementation of typing.List is used instead of the Python 2
backport of the typing module due to non-technical reasons.)

Use CheckedIPAddress instead of 'ip' and 'ip-local' to declare IP
addresses.

https://fedorahosted.org/freeipa/ticket/6392

Reviewed-By: Martin Basti <mbasti@redhat.com>

ipapython/install/typing.py

@@ -0,0 +1,34 @@
+#
+# Copyright (C) 2016  FreeIPA Contributors see COPYING for license
+#
+
+import weakref
+
+import six
+
+_cache = weakref.WeakValueDictionary()
+
+
+class ListMeta(type):
+    def __getitem__(cls, key):
+        if not isinstance(key, type):
+            raise TypeError("Parameters to generic types must be types. "
+                            "Got {!r}.".format(key))
+
+        t = ListMeta(
+            cls.__name__,
+            cls.__bases__,
+            {
+                '__parameters__': (key,),
+                '__init__': cls.__init__,
+            }
+        )
+
+        return _cache.get(key, t)
+
+
+class List(six.with_metaclass(ListMeta, list)):
+    __parameters__ = ()
+
+    def __init__(self, *_args, **_kwargs):
+        raise TypeError("Type List cannot be instantiated; use list() instead")