plugable: support plugin versioning

Allow multiple incompatible versions of a plugin using the same name. The
current plugins are assumed to be version '1'.

The unique identifier of plugins was changed from plugin name to plugin
name and version. By default, the highest version available at build time
is used. If the plugin is an unknown remote plugin, version of '1' is used
by default.

https://fedorahosted.org/freeipa/ticket/4427

Reviewed-By: David Kupka <dkupka@redhat.com>

ipalib/cli.py

@@ -728,6 +728,8 @@ class help(frontend.Local):
 
         # build help topics
         for c in self.api.Command():
+            if c is not self.api.Command[c.name]:
+                continue
             if c.NO_CLI:
                 continue
 
@@ -792,6 +794,8 @@ class help(frontend.Local):
         elif name == "commands":
             mcl = 0
             for cmd in self.Command():
+                if cmd is not self.Command[cmd.name]:
+                    continue
                 if cmd.NO_CLI:
                     continue
                 mcl = max(mcl, len(cmd.name))