TASK_INDEX environment variables are not being set for a job with more than one replica

[sponsology]

Is this a BUG REPORT or FEATURE REQUEST?:

/kind bug

What happened:
When running a job with more than 1 replica, the VC_TASK_INDEX and VK_TASK_INDEX environment variables aren't set in the pod environment.

What you expected to happen:
The *_TASK_INDEX variables to be set.

How to reproduce it (as minimally and precisely as possible):
Submit a job using a spec like

apiVersion: batch.volcano.sh/v1alpha1
kind: Job
metadata:
  name: test-job
spec:
  schedulerName: volcano
  tasks:
    - replicas: 2
      name: test
      template:
        spec:
          containers:
            - image: "ubuntu:18.04"
              name: dev9
              command: ["bash"]
              args: ["-c", "env"]
              resources:
                requests:
                  cpu: "1000m"
                limits:
                  nvidia.com/gpu: 1
          affinity:
            nodeAffinity:
              preferredDuringSchedulingIgnoredDuringExecution:
                - weight: 1
                  preference:
                    matchExpressions:
                      - key: lifecycle
                        operator: In
                        values:
                          - spot

and you can observe the variables are not set

Anything else we need to know?:
No

Environment:

• Volcano Version: master branch as at October 8 2020
• Kubernetes version (use kubectl version): Server Version: version.Info{Major:"1", Minor:"17+", GitVersion:"v1.17.9-eks-4c6976", GitCommit:"4c6976793196d70bc5cd29d56ce5440c9473648e", GitTreeState:"clean", BuildDate:"2020-07-17T18:46:04Z", GoVersion:"go1.13.9", Compiler:"gc", Platform:"linux/amd64"}
• Cloud provider or hardware configuration: AWS EKS
• OS (e.g. from /etc/os-release):

NAME="Amazon Linux"
VERSION="2"
ID="amzn"
ID_LIKE="centos rhel fedora"
VERSION_ID="2"
PRETTY_NAME="Amazon Linux 2"
ANSI_COLOR="0;33"
CPE_NAME="cpe:2.3:o:amazon:amazon_linux:2"
HOME_URL="https://amazonlinux.com/"

• Kernel (e.g. uname -a): Linux ip-10-62-55-52.us-west-2.compute.internal 4.14.198-152.320.amzn2.x86_64 #1 SMP Wed Sep 23 23:57:28 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux
• Install tools: Installed via deployment yaml
• Others:

[hzxuzhonghu]

@sponsology It requires to set plugin to env if you want env set

[stale]

Hello 👋 Looks like there was no activity on this issue for last 90 days.
Do you mind updating us on the status? Is this still reproducible or needed? If yes, just comment on this PR or push a commit. Thanks! 🤗
If there will be no activity for 60 days, this issue will be closed (we can always reopen an issue if we need!).