Increase Unit Test Coverage

[ChristianAtDell]

Description

This PR includes substantial unit test coverage increase across gocsi packages.

GitHub Issues

List the GitHub issues impacted by this PR:

GitHub Issue #
dell/csm#1707

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 80% 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?

opensuse154:~/git/gocsi # go test -cover -race ./...
?       github.com/dell/gocsi/middleware/serialvolume/types     [no test files]
        github.com/dell/gocsi/mock/provider             coverage: 0.0% of statements
        github.com/dell/gocsi/mock              coverage: 0.0% of statements
        github.com/dell/gocsi/mock/service              coverage: 0.0% of statements
ok      github.com/dell/gocsi   6.100s  coverage: 80.3% of statements
ok      github.com/dell/gocsi/context   1.055s  coverage: 82.1% of statements
ok      github.com/dell/gocsi/csc       1.029s
ok      github.com/dell/gocsi/csc/cmd   1.111s  coverage: 82.2% of statements
ok      github.com/dell/gocsi/middleware/logging        1.075s  coverage: 82.4% of statements
ok      github.com/dell/gocsi/middleware/requestid      1.092s  coverage: 82.8% of statements
ok      github.com/dell/gocsi/middleware/serialvolume   1.080s  coverage: 91.9% of statements
ok      github.com/dell/gocsi/middleware/serialvolume/etcd      9.454s  coverage: 80.3% of statements
ok      github.com/dell/gocsi/middleware/specvalidator  1.084s  coverage: 80.7% of statements
ok      github.com/dell/gocsi/testing   40.879s coverage: [no statements]
ok      github.com/dell/gocsi/utils     1.254s  coverage: 80.4% of statements

The only packages not at 80% or above are:

• middleware/serialvolume/types (no functional code, only type definitions)
• mock, mock/service, mock/provider (mock controller client/server, for testing)
• testing (legacy gomega unit tests)

All other packages are at 80% coverage or above.