update validation for core types

[Liujingfang1]

This is the test I did. With type defined as

type MyKindSpec struct {
    Replica int `json:"replica,omitempty"`
    Pod v1.PodTemplate `json:"pod,omitempty"`
}

// MyKindStatus defines the observed state of MyKind
type MyKindStatus struct {
}

// +genclient
// +k8s:deepcopy-gen:interfaces=k8s.io/apimachinery/pkg/runtime.Object

// MyKind
// +k8s:openapi-gen=true
// +resource:path=mykinds
type MyKind struct {
    metav1.TypeMeta   `json:",inline"`
    metav1.ObjectMeta `json:"metadata,omitempty"`

    Spec   MyKindSpec   `json:"spec,omitempty"`
    Status MyKindStatus `json:"status,omitempty"`
}

Then create example yaml as

apiVersion: jingfang.example.com/v1beta1
kind: MyKind
metadata:
  name: mykind-example
spec:
  foo: bar
  replica: 2
  pod:
    name: "something"
    metadata:
      name: "something"

This object passed validation and can be created.

A different example yaml as

apiVersion: jingfang.example.com/v1beta1
kind: MyKind
metadata:
  name: mykind-example
spec:
  foo: bar
  replica: 2
  pod: 3

failed validation and can't be created.

The MyKind "mykind-example" is invalid: []: Invalid value: map[string]interface {}{"spec":map[string]interface {}{"foo":"bar", "pod":3, "replica":2}, "apiVersion":"jingfang.example.com/v1beta1", "kind":"MyKind", "metadata":map[string]interface {}{"uid":"f9639d38-428e-11e8-bcf0-42010a800002", "selfLink":"", "clusterName":"", "name":"mykind-example", "namespace":"default", "generation":1, "creationTimestamp":"2018-04-17T22:30:47Z"}}: validation failure list:
spec.pod in body must be of type object: "integer"