*: implement List and add necessary pieces

[fanminshi]

add NewListOp() factory function to create a listOp
add RuntimeObjectIntoRuntimeObject() which takes in runtime.Object and unmarshal its content into another runtime.Object of the same type.
Implement List that allows user to to query a list of objects.

[fanminshi]

Manual Testing:

	namespace := "default"

	// Test cases for Memcached List
	logrus.Println("TestCase: Get Memcached List")
	l := getMemcachedList("Memcached", "cache.example.com/v1alpha1")
	err := query.List(namespace, l)
	if err != nil {
		logrus.Infof("Failed to get list : %v", err)
	}
	logrus.Println("TestCase: Get NonExistant CR")
	l = getMemcachedList("bad", "cache.example.com/v1alpha1")
	err = query.List(namespace, l)
	if err != nil {
		logrus.Infof("Failed to get list: %v", err)
	}
	logrus.Println("TestCase: Get Memcached List with APIVersion: bad")
	l = getMemcachedList("Memcached", "bad")
	err = query.List(namespace, l)
	if err != nil {
		logrus.Infof("Failed to get list %v : %v", err)
	}

	// Test cases for pod List
	logrus.Println("TestCase: Get Pod List")
	pl := getPodList("Pod", "v1")
	err = query.List(namespace, pl)
	if err != nil {
		logrus.Infof("Failed to get list : %v", err)
	}
	logrus.Println("TestCase: Get Pod List with Option")
	pl = getPodList("Pod", "v1")
	lset := map[string]string{
		"name": "memcached-operator2",
	}
	ls := labels.SelectorFromSet(lset).String()
	lop := &metav1.ListOptions{LabelSelector: ls}
	err = query.List(namespace, pl, query.WithListOptions(lop))
	if err != nil {
		logrus.Infof("Failed to get list : %v", err)
	}
	if len(pl.Items) != 1 {
		logrus.Infof("expect size of the list to be %v, got %v", 1, pl.Size())
	}
	logrus.Println("TestCase: Get Pod List with wrong label")
	pl = getPodList("Pod", "v1")
	lset = map[string]string{
		"name": "bad",
	}
	ls = labels.SelectorFromSet(lset).String()
	lop = &metav1.ListOptions{LabelSelector: ls}
	err = query.List(namespace, pl, query.WithListOptions(lop))
	if err != nil {
		logrus.Infof("Failed to get list : %v", err)
	}
	if len(pl.Items) != 0 {
		logrus.Infof("expect size of the list %b, got %v", 0, pl.Size())
	}

func getMemcachedList(kind, APIVersion string) *v1alpha1.MemcachedList {
	return &v1alpha1.MemcachedList{
		TypeMeta: metav1.TypeMeta{
			Kind:       kind,
			APIVersion: APIVersion,
		},
	}
}

func getPodList(kind, APIVersion string) *v1.PodList {
	return &v1.PodList{
		TypeMeta: metav1.TypeMeta{
			Kind:       kind,
			APIVersion: APIVersion,
		},
	}
}

Output:

time="2018-03-26T19:46:35Z" level=info msg="TestCase: Get Memcached List"
time="2018-03-26T19:46:35Z" level=info msg="TestCase: Get NonExistant CR"
time="2018-03-26T19:46:35Z" level=info msg="Failed to get list: failed to get resource client for (apiVersion:cache.example.com/v1alpha1, kind:bad, ns:default): failed to get resource type: failed to get the resource REST mapping for GroupVersionKind(cache.example.com/v1alpha1, Kind=bad): no matches for cache.example.com/, Kind=bad"
time="2018-03-26T19:46:35Z" level=info msg="TestCase: Get Memcached List with APIVersion: bad"
time="2018-03-26T19:46:35Z" level=info msg="Failed to get list failed to get resource client for (apiVersion:bad, kind:Memcached, ns:default): failed to get resource type: failed to get the resource REST mapping for GroupVersionKind(/bad, Kind=Memcached): no matches for /, Kind=Memcached : %!v(MISSING)"
time="2018-03-26T19:46:35Z" level=info msg="TestCase: Get Pod List"
time="2018-03-26T19:46:35Z" level=info msg="TestCase: Get Pod List with Option"
time="2018-03-26T19:46:35Z" level=info msg="TestCase: Get Pod List with wrong label"

[fanminshi]

PTAL cc/ @hasbro17

[hasbro17]

List lists a list of kubernetes object and then unmarshals the retrieved data into the "into" object.

List retrieves the specified object list and unmarshals the retrieved data into the "into" object.

[hasbro17]

LGTM after nit.