fix(webhook): reject PVC deletion request when dependent snapshots exists

[mittachaitu]

What this PR does / why we need it:
This PR rejects the PVC deletion request when the snapshot exists for the corresponding volume.
When VolumeSnapshot/VolumeSnapshotData exist for particular volume then the deletion of PVC will be errored with the following message

sai@sai:~/Desktop/learn/aws_external_disk$ kubectl delete -f pvc.yml 
Error from server: error when deleting "pvc.yml": admission webhook "admission-webhook.openebs.io" denied the request: snapshots verification failed pvc demo-vol1-claim has '1' snapshot(s)

Note:

• The request will be rejected only if the admission server pod is in running state.
• Irrespective of the ReclaimPolicy of PV, the PVC deletion request will be rejected.

Sample SnapshotExample which will help for reviewers:
volumesnapshot example:

apiVersion: volumesnapshot.external-storage.k8s.io/v1
kind: VolumeSnapshot
metadata:
  annotations:
    kubectl.kubernetes.io/last-applied-configuration: |
      {"apiVersion":"volumesnapshot.external-storage.k8s.io/v1","kind":"VolumeSnapshot","metadata":{"annotations":{},"labels":{"name":"snapshot-demo-csto"},"name":"snapshot-demo-cstor","namespace":"default"},"spec":{"persistentVolumeClaimName":"demo-vol1-claim"}}
  creationTimestamp: "2020-04-15T14:07:06Z"
  generation: 3
  labels:
    SnapshotMetadata-PVName: pvc-c6a09b80-4d3c-4302-ab91-dd6b35dc990d
    SnapshotMetadata-Timestamp: "1586959626455945327"
    name: snapshot-demo-csto
  name: snapshot-demo-cstor
  namespace: default
  resourceVersion: "1199"
  selfLink: /apis/volumesnapshot.external-storage.k8s.io/v1/namespaces/default/volumesnapshots/snapshot-demo-cstor
  uid: 148cf3fb-a999-4298-8541-1c8e3501b318
spec:
  persistentVolumeClaimName: demo-vol1-claim
  snapshotDataName: k8s-volume-snapshot-6459c902-7f22-11ea-ac93-0242ac110004
status:
  conditions:
  - lastTransitionTime: "2020-04-15T14:07:07Z"
    message: Snapshot created successfully
    reason: ""
    status: "True"
    type: Ready
  creationTimestamp: null

VolumeSnapshotData example:

apiVersion: volumesnapshot.external-storage.k8s.io/v1
kind: VolumeSnapshotData
metadata:
  creationTimestamp: "2020-04-15T14:07:07Z"
  generation: 1
  name: k8s-volume-snapshot-6459c902-7f22-11ea-ac93-0242ac110004
  resourceVersion: "1198"
  selfLink: /apis/volumesnapshot.external-storage.k8s.io/v1/volumesnapshotdatas/k8s-volume-snapshot-6459c902-7f22-11ea-ac93-0242ac110004
  uid: a1086239-97a4-4cb2-963f-f8953c1fa4a4
spec:
  openebsVolume:
    capacity: 5G
    snapshotId: pvc-c6a09b80-4d3c-4302-ab91-dd6b35dc990d_snapshot-demo-cstor_1586959626466213150
  persistentVolumeRef:
    kind: PersistentVolume
    name: pvc-c6a09b80-4d3c-4302-ab91-dd6b35dc990d
  volumeSnapshotRef:
    kind: VolumeSnapshot
    name: default/snapshot-demo-cstor-148cf3fb-a999-4298-8541-1c8e3501b318
status:
  conditions:
  - lastTransitionTime: "2020-04-15T14:07:07Z"
    message: Snapshot created successfully
    reason: ""
    status: "True"
    type: Ready
  creationTimestamp: null

Which issue this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close that issue when PR gets merged): fixes #openebs/openebs#2994

Release Note:

• PVC deletion request will be error out if the volume has dependent snapshots(VolumeSnapshot (or) VolumeSnapshotData).

Special notes for your reviewer:

Checklist:

• Fixes #
• Labelled this PR & related issue with documentation tag
• PR messages has document related information
• Labelled this PR & related issue with breaking-changes tag
• PR messages has breaking changes related information
• Labelled this PR & related issue with requires-upgrade tag
• PR messages has upgrade related information
• Commit has unit tests
• Commit has integration tests

[prateekpandey14]

Not remember exactly , does VolumeSnapshotData not have any PV based label ?

[mittachaitu]

The PR description already has an example to make easy reviews

[prateekpandey14]

ok i can see that you have added the full SnapshotData resources ( it was not there before when i reviewed)

[mittachaitu]

metadata added later.

[mittachaitu]

sai@sai:~/gocode/src/github.com/openebs/maya/tests/cstor/snapshot$ ginkgo -v -- -kubeconfig=/var/run/kubernetes/admin.kubeconfig -cstor-maxpools=1 -cstor-replicas=1
Running Suite: Test cstor volume snapshot provisioning
======================================================
Random Seed: 1586967695
Will run 1 of 1 specs

STEP: waiting for maya-apiserver pod to come into running state
STEP: waiting for openebs-provisioner pod to come into running state
STEP: Verifying 'admission-server' pod status as running
STEP: building a namespace
STEP: creating a namespace
[cstor] TEST SNAPSHOT PROVISIONING when cstor pvc with replicacount n is created 
  should create cstor volume target pod
  /home/sai/gocode/src/github.com/openebs/maya/tests/cstor/snapshot/snapshot_test.go:96
STEP: building spc object
STEP: creating storagepoolclaim
STEP: verifying healthy csp count
STEP: building a CAS Config with generated SPC name
STEP: building storageclass object
STEP: creating storageclass
STEP: building a persistentvolumeclaim
STEP: creating cstor persistentvolumeclaim
STEP: verifying volume target pod count as 1
STEP: verifying cstorvolume replica count
STEP: verifying pvc status as bound
STEP: building a cstor volume snapshot
STEP: creating cstor volume snapshot
STEP: verifying snapshot status as ready
STEP: Deleting PersistentVolumeClaim Should Reject the Request Because Of Snapshot Existence
STEP: deleting cstor volume snapshot
STEP: verifying deleted snapshot
STEP: Verifying deletion of snapshotdata
STEP: deleting above pvc
STEP: verifying target pod count as 0
STEP: verifying deleted pvc
STEP: verifying if cstorvolume is deleted
STEP: deleting resources created for cstor volume snapshot provisioning
STEP: deleting storagepoolclaim
STEP: deleting storageclass

• [SLOW TEST:111.625 seconds]
[cstor] TEST SNAPSHOT PROVISIONING
/home/sai/gocode/src/github.com/openebs/maya/tests/cstor/snapshot/snapshot_test.go:36
  when cstor pvc with replicacount n is created
  /home/sai/gocode/src/github.com/openebs/maya/tests/cstor/snapshot/snapshot_test.go:95
    should create cstor volume target pod
    /home/sai/gocode/src/github.com/openebs/maya/tests/cstor/snapshot/snapshot_test.go:96
------------------------------
STEP: deleting namespace

Ran 1 of 1 Specs in 111.682 seconds
SUCCESS! -- 1 Passed | 0 Failed | 0 Pending | 0 Skipped
PASS

Ginkgo ran 1 suite in 1m57.727257024s
Test Suite Passed

[mynktl]

looks good to me

[shubham14bajpai]

LGTM