Add logic for openebs namespace determination from cli code

[Abhinandan-Purkait]

What does this PR do?

• This PR adds logic to determine the openebs namespace using the cas-type from engine specific components.
• This PR solves the problem of existence two namespaces, by determining one from the code itself.
• This PR also adds a flag openebs-namespace which can allow user to enter the namespace by himself in case the logic fails.
• Currently the logic is made to work for cstor only.

The new flag

❯ kubectl openebs describe pvc -h

Flags:
  -h, --help                       help for pvc
      --openebs-namespace string   to read the openebs namespace from user.
                                   If not provided it is determined from components.

Usage:-

kubectl openebs describe pvc cstor-vol-1 cstor-vol-2 -n storage --openebs-namespace=openebs

Closes #18

[vharsh]

Awesome PR, just a minor code simplification suggestion

[vharsh]

lgtm, had minor suggestions