fix pvc deletetion

[AdheipSingh]

Fixes #186

Description

---

This PR has:

• been tested on a real K8S cluster to ensure creation of a brand new Druid cluster works.
• been tested for backward compatibility on a real K*S cluster by applying the changes introduced here on an existing Druid cluster. If there are any backward incompatible changes then they have been noted in the PR description.
• added comments explaining the "why" and the intent of the code wherever would not be obvious for an unfamiliar reader.
• added documentation for new or modified features or behaviors.

---

@himanshug ##### Key changed/added files in this PR * `handler.go`

[AdheipSingh]

On further debug, i see that in case you have a custom pvc mounted on any of the nodes, the operator wont remove any sts mounted pvc ( somehow thats where i missed out this bug, since i am using custom pvc too )

Regardless, its fine now. I will be working on getting some integration tests on a live k8s cluster. I tried to catch the same error with smoke tests but it cant catch such errors.

@himanshug Do you think we need to cut a release for this bug fix ? since 0.0.6 will have this bug, it might affect users.

[himanshug]

pushed a patch release 0.0.6.1 , thanks!

[AdheipSingh]

@himanshug awesome !