Test Coverage Improvement

[TJM]

Current:

ok  	github.com/jfrog/artifactory-secrets-plugin	0.508s	coverage: 62.7% of statements

See coverage.html file (inside coverage.html.gz) for details. Generated with: go tool cover -html=coverage.txt -o ~/Downloads/coverage.html.

Most of the uncovered code is inside if err != nil sections, which I think we can cover with mock tests. Some of the bigger sections are like the "renew" and "revoke" which are super easy in acceptance, but could also be mocked.