fix golint issues in core/proc (#502)

core/proc/shutdown.go

@@ -24,14 +24,19 @@ var (
 	delayTimeBeforeForceQuit = waitTime
 )
 
+// AddShutdownListener adds fn as a shutdown listener.
+// The returned func can be used to wait for fn getting called.
 func AddShutdownListener(fn func()) (waitForCalled func()) {
 	return shutdownListeners.addListener(fn)
 }
 
+// AddWrapUpListener adds fn as a wrap up listener.
+// The returned func can be used to wait for fn getting called.
 func AddWrapUpListener(fn func()) (waitForCalled func()) {
 	return wrapUpListeners.addListener(fn)
 }
 
+// SetTimeToForceQuit sets the waiting time before force quitting.
 func SetTimeToForceQuit(duration time.Duration) {
 	delayTimeBeforeForceQuit = duration
 }