Fixes an issue with hosts having an IPv6 address on localhost

- When 'getent hosts localhost' returns '::1' the creation of the
  listener fails because of the port parsing which uses ":" as a
separator
- Use of net.SplitHostPort() to do the job
- Adding unit tests to ensure that the creation succeeds
- On docker.go: adds a test on the presence the socat command which was
  failing silenty if not installed

- Code Review 1
  - Fixed typo on Expected
  - The UT now fails if the PortForwarder could not be created

- Code Review 2
  - Simplify socat error message
  - Changing t.Fatal to to.Error on unit tests

- Code Review 3
  - Removing useless uses cases in unit tests

- Code Review 4
  - Removing useless initiliasiation of PortForwarder
  - Changing error message

- Code Review 5
  - Simplifying TestCast struct
  - Adding addition test in one test case
  - Closing the listener

- Code Review 6
  - Improving unit test

pkg/client/portforward/portforward_test.go

@@ -209,14 +209,16 @@ func (s *fakeUpgradeStream) Headers() http.Header {
 	return http.Header{}
 }
 
+type TestCase struct {
+	Hostname                string
+	Protocol                string
+	ShouldRaiseError        bool
+	ExpectedListenerAddress string
+}
+
 func TestGetListener(t *testing.T) {
 	var pf PortForwarder
-	testCases := []struct {
+	testCases := []TestCase{
-		Hostname                string
-		Protocol                string
-		ShouldRaiseError        bool
-		ExpectedListenerAddress string
-	}{
 		{
 			Hostname:                "localhost",
 			Protocol:                "tcp4",
@@ -235,12 +237,6 @@ func TestGetListener(t *testing.T) {
 			ShouldRaiseError:        false,
 			ExpectedListenerAddress: "::1",
 		},
-		{
-			Hostname:                "localhost",
-			Protocol:                "tcp6",
-			ShouldRaiseError:        false,
-			ExpectedListenerAddress: "::1",
-		},
 		{
 			Hostname:         "[::1]",
 			Protocol:         "tcp4",
@@ -253,6 +249,20 @@ func TestGetListener(t *testing.T) {
 		},
 	}
 
+	// On some linux systems, ::1 does not resolve to localhost but to localhost6 or
+	// ip6-localhost. To make the test case portable, we need to do a reverse lookup on ::1 and
+	// trying to bind a port with the name.
+	names, err := net.LookupAddr("::1")
+	if err == nil && len(names) > 0 {
+		ipv6TestCase := TestCase{
+			Hostname:                names[0],
+			Protocol:                "tcp6",
+			ShouldRaiseError:        false,
+			ExpectedListenerAddress: "::1",
+		}
+		testCases = append(testCases, ipv6TestCase)
+	}
+
 	for i, testCase := range testCases {
 		expectedListenerPort := "12345"
 		listener, err := pf.getListener(testCase.Protocol, testCase.Hostname, &ForwardedPort{12345, 12345})