ssh/test: set a timeout and WaitDelay on sshd subcommands

This uses a copy of testenv.Command copied from the main repo, with
light edits to allow the testenv helpers to build with Go 1.19.

The testenv helper revealed an exec.Command leak in TestCertLogin, so
we also fix that leak and simplify server cleanup using
testing.T.Cleanup.

For golang/go#60099.
Fixes golang/go#60343.

Change-Id: I7f79fcdb559498b987ee7689972ac53b83870aaf
Reviewed-on: https://go-review.googlesource.com/c/crypto/+/496935
Auto-Submit: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Roland Shoemaker <roland@golang.org>
Run-TryBot: Bryan Mills <bcmills@google.com>

ssh/test/forward_unix_test.go

@@ -23,7 +23,6 @@ type closeWriter interface {
 
 func testPortForward(t *testing.T, n, listenAddr string) {
 	server := newServer(t)
-	defer server.Shutdown()
 	conn := server.Dial(clientConfig())
 	defer conn.Close()
 
@@ -120,7 +119,6 @@ func TestPortForwardUnix(t *testing.T) {
 
 func testAcceptClose(t *testing.T, n, listenAddr string) {
 	server := newServer(t)
-	defer server.Shutdown()
 	conn := server.Dial(clientConfig())
 
 	sshListener, err := conn.Listen(n, listenAddr)
@@ -162,10 +160,9 @@ func TestAcceptCloseUnix(t *testing.T) {
 // Check that listeners exit if the underlying client transport dies.
 func testPortForwardConnectionClose(t *testing.T, n, listenAddr string) {
 	server := newServer(t)
-	defer server.Shutdown()
-	conn := server.Dial(clientConfig())
+	client := server.Dial(clientConfig())
 
-	sshListener, err := conn.Listen(n, listenAddr)
+	sshListener, err := client.Listen(n, listenAddr)
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -184,14 +181,10 @@ func testPortForwardConnectionClose(t *testing.T, n, listenAddr string) {
 
 	// It would be even nicer if we closed the server side, but it
 	// is more involved as the fd for that side is dup()ed.
-	server.clientConn.Close()
+	server.lastDialConn.Close()
 
-	select {
-	case <-time.After(1 * time.Second):
-		t.Errorf("timeout: listener did not close.")
-	case err := <-quit:
-		t.Logf("quit as expected (error %v)", err)
-	}
+	err = <-quit
+	t.Logf("quit as expected (error %v)", err)
 }
 
 func TestPortForwardConnectionCloseTCP(t *testing.T) {