Print Stack API version in version command

* Resolve Stack API using Kubernetes discovering API
* Refactor Kubernetes flags parsing

Signed-off-by: Silvin Lubecki <silvin.lubecki@docker.com>

kubernetes/check_test.go

@@ -0,0 +1,49 @@
+package kubernetes
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+)
+
+func TestGetStackAPIVersion(t *testing.T) {
+	var tests = []struct {
+		description   string
+		groups        *metav1.APIGroupList
+		err           bool
+		expectedStack StackVersion
+	}{
+		{"no stack api", makeGroups(), true, ""},
+		{"v1beta1", makeGroups(groupVersion{"compose.docker.com", []string{"v1beta1"}}), false, StackAPIV1Beta1},
+	}
+
+	for _, test := range tests {
+		version, err := getAPIVersion(test.groups)
+		if test.err {
+			require.Error(t, err)
+		} else {
+			require.NoError(t, err)
+		}
+		assert.Equal(t, test.expectedStack, version)
+	}
+}
+
+type groupVersion struct {
+	name     string
+	versions []string
+}
+
+func makeGroups(versions ...groupVersion) *metav1.APIGroupList {
+	groups := make([]metav1.APIGroup, len(versions))
+	for i := range versions {
+		groups[i].Name = versions[i].name
+		for _, v := range versions[i].versions {
+			groups[i].Versions = append(groups[i].Versions, metav1.GroupVersionForDiscovery{Version: v})
+		}
+	}
+	return &metav1.APIGroupList{
+		Groups: groups,
+	}
+}