NDM should never bind BD with empty bd tag value to any BDC

[sonasingh46]

A BD if tagged with an empty value should never be bound and this restriction should be enforced from the NDM.
This can help ensure that any other component(e.g cStor ) that utilizes NDM for disk management and discovery is not able to use a disk if someone wants to reserve it.
Although cStor does not uses BD with an empty tag, this should be enforced from the backend NDM

[sonasingh46]

@kmova @akhilerm -- What are your thoughts on this one?

[akhilerm]

A check can be added in NDM operator such that a blockdevice resource with openebs.io/block-device-tag= can never be claimed.
The check can be added here in the filtering logic.

[akhilerm]

openebs-archive/node-disk-manager#500 has been merged which contains the changes for implementing this feature.

The new changes includes:

• blockdevices with an empty block-device-tag value can never be claimed.