ostree: Add notification handler to wait for signature

This script can be used as a notification handler. For most messages it
does nothing, but when it sees a new commit in an ostree repo, it will
wait for a signature of the new commit to appear.

This is useful for building images later so that they include the
signature as well.

Fixes: https://pagure.io/pungi/issue/650
Signed-off-by: Lubomír Sedlář <lsedlar@redhat.com>

setup.py

@@ -43,6 +43,7 @@ setup(
         'bin/pungi-koji',
         'bin/pungi-make-ostree',
         'bin/pungi-patch-iso',
+        'bin/pungi-wait-for-signed-ostree-handler',
 
         'contrib/yum-dnf-compare/pungi-compare-depsolving',
     ],