Add script to orchestrate multiple composes

It may make sense to break a big compose into smaller chunks that can be
done independently. This script allows describing the smaller parts,
runs them with correct dependencies and arranges the result to look like
a single big compose.

All parts use the same koji event, that is either obtained from Koji, or
from command line argument.

JIRA: COMPOSE-2654
Signed-off-by: Lubomír Sedlář <lsedlar@redhat.com>

setup.py

@@ -43,6 +43,7 @@ setup(
         'bin/pungi-gather',
         'bin/pungi-koji',
         'bin/pungi-make-ostree',
+        'bin/pungi-orchestrate',
         'bin/pungi-patch-iso',
         'bin/pungi-wait-for-signed-ostree-handler',