Support for Partial Success Backup

[prashanthpx]

What type of PR is this? Enhancement

What this PR does / why we need it: Adds support for Partial Success backup

Does this PR change a user-facing CRD or CLI?: No

Is a release note needed?: No

Does this change need to be cherry-picked to a release branch?: Yes

Note: As part of release notes, we will add this

[prashanthpx]

@siva-portworx @vsundarraj-px all review comments addressed. Also did cleanup on partialFailed/partialSuccess variable so few comments gets addressed as part of it. Pls review the same

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 0% with 9 lines in your changes are missing coverage. Please review.

Project coverage is 38.18%. Comparing base (d4fd2d8) to head (9dc61b8).

:exclamation: Current head 9dc61b8 differs from pull request most recent head 123f8ac

Please upload reports for the commit 123f8ac to get more accurate results.

Files	Patch %	Lines
drivers/volume/portworx/portworx.go	0.00%	9 Missing :warning:

Additional details and impacted files

@@              Coverage Diff              @@
##           pxb-2.7.2    #1716      +/-   ##
=============================================
- Coverage      38.23%   38.18%   -0.05%     
=============================================
  Files             51       51              
  Lines          11381    11388       +7     
=============================================
- Hits            4351     4348       -3     
- Misses          6642     6651       +9     
- Partials         388      389       +1     

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[prashanthpx]

Added few more comments

@vsundarraj-px All comments are addressed, let me know if aything else needs to be addressed. I had seen your approval before but it still shows changes requested.