Use writable snapshot when cloning from PVC or snapshot

[donatwork]

Description

Currently waiting for unit test coverage to increase before submitting PR but please review...

This PR solves the issue where cloning of large active source volumes are taking a long time. This may cause timeouts in some use cases. The cause of the timeout is due to the current process of cloning where a copy operation is used to copy from the source location to the destination. This is a slow operation.

The solution is to use snapshots to get a point in time copy, which is more consistent that copying an active volume, and then create a writable snapshot of the first snapshot. In this way the cloning operation can be reduced from minutes, hours perhaps, to seconds.

Some changes were made to CreateVolume and DeleteVolume to deal with writable snapshots.

 

GitHub Issues

List the GitHub issues impacted by this PR:

GitHub Issue #
dell/csm#1763

Checklist:

• I have performed a self-review of my own code to ensure there are no formatting, vetting, linting, or security issues
• I have verified that new and existing unit tests pass locally with my changes
• I have not allowed coverage numbers to degenerate
• I have maintained at least 90% code coverage
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• Backward compatibility is not broken

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Please also list any relevant details for your test configuration

Ran the following test cases:

Test Case	Info	Status	Comments
create new pvc		PASS
delete standalone pvc		PASS
create clone of pvc		PASS
delete clone of pvc		PASS
delete source while cloned	clone should remain	PASS
create two clones of source		PASS
delete one of two clones	validate correct clone deleted	PASS
create clone of clone	should fail gracefully?	PASS?	pvc in pending, unsupported operation in logs
create snapshot while source is cloned		PASS
create RO clone of snapshot		PASS
create RW clone of snapshot		PASS
delete clones of source pvc	validate correct clones deleted	PASS
delete source pvc while snapshots exist	should fail gracefully	PASS
delete RW clone of snapshot		PASS
delete RO clone of snapshot		PASS

[donatwork]

Withdrawing PR until decision is made on the solution.