bump(github.com/coreos/go-systemd): c57eef5766c6319c580d8dbfa046abf1c66a0553
fix(agent): clean up when stopping a Job

* clear job state from the registry when instructed to stop
* remove unit from dbus subscription when instructed to stop
Merge pull request #76 from bcwaldon/agent-cleanup

Clean up job state and drop from dbus subscription set