libct/int: add TestFdLeaksSystemd

Add a test to check that container.Run do not leak file descriptors.

Before the previous commit, it fails like this:

    exec_test.go:2030: extra fd 8 -> socket:[659703]
    exec_test.go:2030: extra fd 11 -> socket:[658715]
    exec_test.go:2033: found 2 extra fds after container.Run

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

libcontainer/integration/exec_test.go

@@ -1963,6 +1963,14 @@ func TestCGROUPHost(t *testing.T) {
 }
 
 func TestFdLeaks(t *testing.T) {
+	testFdLeaks(t, false)
+}
+
+func TestFdLeaksSystemd(t *testing.T) {
+	testFdLeaks(t, true)
+}
+
+func testFdLeaks(t *testing.T, systemd bool) {
 	if testing.Short() {
 		return
 	}
@@ -1979,7 +1987,10 @@ func TestFdLeaks(t *testing.T) {
 	_, err = pfd.Seek(0, 0)
 	ok(t, err)
 
-	config := newTemplateConfig(&tParam{rootfs: rootfs})
+	config := newTemplateConfig(&tParam{
+		rootfs:  rootfs,
+		systemd: systemd,
+	})
 	buffers, exitCode, err := runContainer(config, "", "true")
 	ok(t, err)