Comment 3 for bug 980037

I'd like to reopen this to address issue with systemd notifications https://bugzilla.redhat.com/show_bug.cgi?id=820448#c2
My proposed patch builds on 6c5f7d9e10f059e2bc1e56ea2d4e32a7e4cadc8b and reuses "onready" configuration parameter like this:
1. try import_module(CONF.onready) and call mod.notify() for in process notification (see above BZ comment for an example)
2. fallback to the current behaviour, running a shell command