Adds identity to task in VolumePolicy
Adds identity to task in VolumePolicy

1. Why is this change necessary ?

Operator must set identity to a task & can refer to the
task result using this identity. This removes the
dependency on order index of a task.

fixes https://github.com/openebs/openebs/issues/1191

2. How does this change address the issue ?

- Modifications are done that makes use of task
identity mentioned in VolumePolicy

3. How to verify this change ?

- Use VolumePolicy with task identity & make use of
 these identity in the task templates

4. What side effects does this change have ?

- None

```yaml
apiVersion: openebs.io/v1alpha1
kind: VolumePolicy
metadata:
  name: openebs-policy-0.6.0
spec:
  policies:
  - name: VolumeMonitor
    enabled: "true"
    value: openebs/m-exporter:0.5.0
  - name: ControllerImage
    value: openebs/jiva:0.5.0
  - name: ReplicaImage
    value: openebs/jiva:0.5.0
  - name: ReplicaCount
    value: "2"
  - name: StoragePool
    value: ssd
  run:
    searchNamespace: default
    tasks:
    - template: volume-service-0.6.0
      identity: vsvc
    - template: volume-path-0.6.0
      identity: vpath
    - template: volume-controller-0.6.0
      identity: vctrl
    - template: volume-replica-0.6.0
      identity: vrep
```

- snippet of a openebs replica template that makes use of
identity in determining the service IP

```yaml
          containers:
          - args:
            - replica
            - --frontendIP
            - {{ .TaskResult.vsvc.serviceIP }}
            - --size
            - {{ .Volume.capacity }}
            - /openebs
            command:
            - launch
            image: {{ .Policy.ReplicaImage.value }}
            name: {{ .Volume.owner }}-rep-con
```

- similarly snippet of the openebs replica template that makes of
identity in determining the path

```yaml
          volumes:
          - name: openebs
            hostPath:
              path: {{ .TaskResult.vpath.storagePoolPath }}/{{ .Volume.owner }}
```

Signed-off-by: amitkumardas <afede79b701ad618a6c07974063f642c07c6d765@cloudbyte.com>

yudaykiran/openebs