ctlsock: don't Warn() on closed socket

This Warn() is causing panics in the test suite
on MacOS: #213

internal/ctlsock/ctlsock_serve.go

@@ -60,10 +60,10 @@ func (ch *ctlSockHandler) acceptLoop() {
 	for {
 		conn, err := ch.socket.Accept()
 		if err != nil {
-			// TODO Can this warning trigger when the socket it closed on
-			// program exit? I have never observed it, but the documentation
-			// says that Close() unblocks Accept().
-			tlog.Warn.Printf("ctlsock: Accept error: %v", err)
+			// This can trigger on program exit with "use of closed network connection".
+			// Special-casing this is hard due to /~https://github.com/golang/go/issues/4373
+			// so just don't use tlog.Warn to not cause panics in the tests.
+			tlog.Info.Printf("ctlsock: Accept error: %v", err)
 			break
 		}
 		go ch.handleConnection(conn.(*net.UnixConn))