Unit test cases for block volume and block volume snapshot

[nguptaopensds]

What type of PR is this?

Uncomment only one /kind <> line, hit enter to put that in a new line, and remove leading whitespace from that line:

/kind new feature
/kind bug fix
/kind cleanup
/kind revert change
/kind design
/kind documentation

/kind enhancement

What this PR does / why we need it:
Adding unit test cases for block volumes

Which issue(s) this PR fixes:
#1270

Fixes #

Test Report Added?:

Uncomment only one /kind <> line, hit enter to put that in a new line, and remove leading whitespace from that line:

/kind TESTED

/kind NOT-TESTED

Test Report:

Special notes for your reviewer:

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 39.67%. Comparing base (7eb8236) to head (759db3e).
Report is 5 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1299      +/-   ##
==========================================
- Coverage   41.48%   39.67%   -1.81%     
==========================================
  Files          53       53              
  Lines        7752     6966     -786     
==========================================
- Hits         3216     2764     -452     
+ Misses       4021     3662     -359     
- Partials      515      540      +25     

see 53 files with indirect coverage changes

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[kumarashit]

LGTM