fix(controller): fix nil pointer dereference in BDC controller due to non existent BD

[akhilerm]

Signed-off-by: Akhil Mohan akhil.mohan@mayadata.io

Why is this PR required? What issue does it fix?:
When a Claimed BD is manually deleted by removing the finalizer, and later when the user
tries to delete BDC, NDM operator will continuously crash. This because NDM operator
tries to release a non existent BD.

What this PR does?:
adds a check to throw an error when the claimed BD is not found. This PR also adds an event to BDC when BlockDevice is not found.

Does this PR require any upgrade changes?:
No

If the changes in this PR are manually verified, list down the scenarios covered::

Any additional information for your reviewer? :
Mention if this PR is part of any design or a continuation of previous PRs

Checklist:

• Fixes panic in NDM operator: blockdeviceclaim.(*ReconcileBlockDeviceClaim).isDeviceRequestedByThisDeviceClaim(...) #439
• PR Title follows the convention of <type>(<scope>): <subject>
• Has the change log section been updated?
• Commit has unit tests
• Commit has integration tests
• (Optional) Are upgrade changes included in this PR? If not, mention the issue/PR to track:
• (Optional) If documentation changes are required, which issue on https://github.com/openebs/openebs-docs is used to track them:

[codecov-commenter]

Codecov Report

Merging #479 into master will decrease coverage by 0.04%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master     #479      +/-   ##
==========================================
- Coverage   40.40%   40.35%   -0.05%     
==========================================
  Files          72       72              
  Lines        3527     3531       +4     
==========================================
  Hits         1425     1425              
- Misses       1993     1997       +4     
  Partials      109      109              

Impacted Files	Coverage Δ
...er/blockdeviceclaim/blockdeviceclaim_controller.go	39.24% <0.00%> (-0.87%)	⬇️

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