plugin/file: shutdown reload goroutine (#1571)

* plugin/file: shutdown reload goroutine

Shutdown the z.Reload() routine (if started in the first place) on
shutdow and reload.

Fixes #1508

* Must be put in c.OnShutdown()

* up test coverage

plugin/auto/zone.go

@@ -60,8 +60,8 @@ func (z *Zones) Add(zo *file.Zone, name string) {
 func (z *Zones) Remove(name string) {
 	z.Lock()
 
-	if zo, ok := z.Z[name]; ok && !zo.NoReload {
-		zo.ReloadShutdown <- true
+	if zo, ok := z.Z[name]; ok {
+		zo.OnShutdown()
 	}
 
 	delete(z.Z, name)