Added a small delay after monitor closing

This is a countermeasure for kernel/firwmare bugs:
resources may take a few milliseconds to actually get freed for real
after killing the process, or even after a regular closing.
This delay makes the caller more resilient to this kind of issues.

Author: cmaglie

Diff for: arduino/monitor/monitor.go

@@ -298,7 +298,15 @@ func (mon *PluggableMonitor) Close() error {
 
 // Quit terminates the monitor. No more commands can be accepted by the monitor.
 func (mon *PluggableMonitor) Quit() error {
-	defer mon.killProcess() // ensure that killProcess is called in any case...
+	defer func() {
+		mon.killProcess() // ensure that killProcess is called in any case...
+
+		// This is a countermeasure for kernel/firwmare bugs:
+		// resources may take a few milliseconds to actually get freed for real
+		// after killing the process, or even after a regular closing.
+		// This delay makes the caller more resilient to this kind of issues.
+		time.Sleep(500 * time.Millisecond)
+	}()
 
 	if err := mon.sendCommand("QUIT\n"); err != nil {
 		return err