Move time.Sleep call in turbotunnel test

An update the the kcp-go library removes the guarantee that all data
written to a KCP connection will be flushed before the connection is
closed. Moving the sleep call has no impact on the integrity of the
tests, and gives the connection time to flush data before the connection
is closed.

See https://github.com/xtaci/kcp-go/issues/273

common/turbotunnel/queuepacketconn_test.go

@@ -208,14 +208,16 @@ func TestQueuePacketConnWriteToKCP(t *testing.T) {
 			panic(err)
 		}
 
+		// A sleep after the Write makes buffer reuse more likely, and is needed
+		// to allow time for flushing all bytes written to the connection before close.
+		// This is not guaranteed by kcp-go. See https://github.com/xtaci/kcp-go/issues/273
+		time.Sleep(100 * time.Millisecond)
+
 		err = conn.Close()
 		if err != nil {
 			panic(err)
 		}
 
-		// A sleep after the Write makes buffer reuse more likely.
-		time.Sleep(100 * time.Millisecond)
-
 		if len(transcript.Transcript) == 0 {
 			panic("empty transcript")
 		}