Add comprehensive unit tests for revoke and installations functionality

- Add revoke_test.go with tabular tests covering all revoke functionality
- Add installations_test.go with comprehensive test coverage
- Test successful token revocation with various hostname formats
- Test error handling for HTTP status codes (401, 403, 404, 500, etc.)
- Test network errors and edge cases
- Mock HTTP requests using httpmock library
- Follow existing test patterns from generate_test.go
- All tests pass with full coverage of implemented features

Author: Link-