Support CronJob

[TommyLike]

1. Add CronJob support with yaml (create volcano job every minute)

apiVersion: batch.volcano.sh/v1alpha1
kind: CronJob
metadata:
  name: test-cronjob
spec:
  schedule: "*/1 * * * *"
  template:
    minAvailable: 2
    schedulerName: kube-batch
    tasks:
      - replicas: 2
        template:
          metadata:
            name: web
          spec:
            containers:
              - image: nginx
                imagePullPolicy: IfNotPresent
                name: nginx
            restartPolicy: OnFailure

2. Add AdmissionValidation for CronJob
3. Support cronjob in helm chart
4. Add E2E tests for cronjob

for #41

[k82cn]

Please split this huge PR into smaller ones, e.g. API, admission, controller, e2e and so on.

[TommyLike]

sure!