plugin/forward: make Yield not block (#3336)

* plugin/forward: may Yield not block

Yield may block when we're super busy with creating (and looking) for
connection. Set a small timeout on Yield, to skip putting the connection
back in the queue.

Use persistentConn troughout the socket handling code to be more
consistent.

Signed-off-by: Miek Gieben <miek@miek.nl>

Dont do

Signed-off-by: Miek Gieben <miek@miek.nl>

* Set used in Yield

This gives one central place where we update used in the persistConns

Signed-off-by: Miek Gieben <miek@miek.nl>

plugin/forward/setup.go

@@ -54,14 +54,11 @@ func (f *Forward) OnStartup() (err error) {
 // OnShutdown stops all configured proxies.
 func (f *Forward) OnShutdown() error {
 	for _, p := range f.proxies {
-		p.close()
+		p.stop()
 	}
 	return nil
 }
 
-// Close is a synonym for OnShutdown().
-func (f *Forward) Close() { f.OnShutdown() }
-
 func parseForward(c *caddy.Controller) (*Forward, error) {
 	var (
 		f   *Forward