code coverage improvement for isiService.go file

[meggm]

Description

This PR is to enhance the code-coverage for isiService.go file in CSI-PowerScale repo. Target to reach is 80%
The function "GetExportsWithResume" is commented as this is used as part ListVolumesAPI which is also commented.
There is no other API which uses this function. Once the ListVolumes API is implemented then this function can be uncommented.

Existing coverage:
overall - 67.6%
isiService.go - 72.9%

With This PR:
overall - 68.7%
isiService.go - 80.5%

GitHub Issues

List the GitHub issues impacted by this PR:

GitHub Issue #
dell/csm#350

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?

Changes are done for unit test cases

• Test A
• Test B

[shefali-malhotra]

LGTM