Make NodePublish mount idempotent

[wongma7]

/kind bug

What happened? as of kubernetes 1.20, kubelet doesn't check if the target path exists or is mounted for us kubernetes/kubernetes#88759 . path existence should be idempotent i.e. if path already exists, NodeStage/NodePublish should not error. mount should be idempotent i.e. if the thing that's supposed to be mounted at the path is already there then NodeStage/NodePublish should not error

NodeStage:

• path existence idempotent

  aws-ebs-csi-driver/pkg/driver/node.go

  Line 175 in 951bafe

  exists, err := d.mounter.PathExists(target)

• mount idempotent

  aws-ebs-csi-driver/pkg/driver/node.go

  Line 203 in 951bafe

  klog.V(4).Infof("NodeStageVolume: volume=%q already staged", volumeID)

NodePublish*:

• path existence idempotent

  aws-ebs-csi-driver/pkg/driver/mount_linux.go

  Line 56 in 951bafe

  if !os.IsExist(err) {

• mount idempotent

  aws-ebs-csi-driver/pkg/driver/node.go

  Line 627 in 951bafe

  return status.Errorf(codes.Internal, "Could not mount %q at %q: %v", source, target, err)

What you expected to happen?

How to reproduce it (as minimally and precisely as possible)?

Anything else we need to know?:

Environment

• Kubernetes version (use kubectl version):
• Driver version: