Agent defers to daemon to advise when ready

The a.ready channel is still useful to synchronize the access to a.daemon,
preventing nil pointer access when the deamon is not yet initialized.
Checking for nil is still needed, as the a.ready channel may be closed without ever serving.

windows-agent/cmd/ubuntu-pro-agent/agent/agent.go

@@ -186,6 +186,10 @@ func (a *App) Quit() {
 // Note: we need to use a pointer to not copy the App object before the daemon is ready, and thus, creates a data race.
 func (a *App) WaitReady() {
 	<-a.ready
+	if a.daemon == nil {
+		return
+	}
+	a.daemon.WaitReady()
 }
 
 // RootCmd returns a copy of the root command for the app. Shouldn't be in general necessary apart when running generators.