Install both hub and builder plugins.

This is a different take at https://pagure.io/koji/pull-request/45

Instead of installing just the runroot builder plugin explicitly, here we
separate the plugins out into hub and builder plugins explicitly and install
each type in turn.

plugins/echo.py

@@ -1,15 +0,0 @@
-# Example Koji callback
-# Copyright (c) 2009-2014 Red Hat, Inc.
-# This callback simply logs all of its args using the logging module
-#
-# Authors:
-#     Mike Bonnet <mikeb@redhat.com>
-
-from koji.plugin import callbacks, callback, ignore_error
-import logging
-
-@callback(*callbacks.keys())
-@ignore_error
-def echo(cbtype, *args, **kws):
-    logging.getLogger('koji.plugin.echo').info('Called the %s callback, args: %s; kws: %s',
-                                               cbtype, str(args), str(kws))