fix the matching logic for the imagePullSecret in ImagePullJob

[zmberg]

Ⅰ. Describe what this PR does

apiVersion: apps.kruise.io/v1alpha1
kind: ImagePullJob
spec:
  image: registry.private.com/app/nginx:1.9.1   # [required] image to pull
  pullSecrets:
  - app-secret

If the secret app-secret is configured as shown below, the ImagePullJob will fail to match, resulting in a failed image pull.

apiVersion: v1
data:
  .dockerconfigjson: {"auths":{"registry.private.com/app":{"username":"echoserver","password":"test","auth":"ZWNob3NlcnZlcjp0ZXN0"}}}
kind: Secret
metadata:
     name: app-secret
type: kubernetes.io/dockerconfigjson

[furykerry]

/lgtm

[furykerry]

/approve

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