Added FileSystem snapshot test scenarios

[ashleyvjoy]

Description

Added new testcases in integration test to create/delete File System snapshots for NFS support

GitHub Issues

List the GitHub issues impacted by this PR:

| GitHub Issue # |
| dell/csm#763 |

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

• Test A- Successfully executed the new scenarios with 4.0 array. The FS snapshots are created/deleted successfully. When executed with 3.6 array which does not have NFS support, the test-scenarios will exit with a message that array does not support NFS

test1.txt