dbus/methods: don't write blocking to jobListener channel

When handling the jobComplete signal, only try to write to the channel
and do not block on the channel write. If nothing reads from this
channel, the function blocks forever and makes it impossible to start
new jobs.

Fixes coreos#429

dbus/methods.go

@@ -45,7 +45,10 @@ func (c *Conn) jobComplete(signal *dbus.Signal) {
 	c.jobListener.Lock()
 	out, ok := c.jobListener.jobs[job]
 	if ok {
-		out <- result
+		select {
+		case out <- result:
+		default:
+		}
 		delete(c.jobListener.jobs, job)
 	}
 	c.jobListener.Unlock()