Refactor pkg_vuln module

[s-kenji]

Description

• Refactor pkg_vlun module
• Split the functions to output files into an exporter module.
• Add test cases for pkg_vlun module
  • Previously we reused test files for dockerfile scan result. So created new test files to cover code branches in pkg_vlun module as much as possible.
• Add unit test cases to verify exported csv/markdown files.
  • Compare test csv/markdown files generated before this refactoring (modified format of markdown files slightly) with generated files in the refactored logic.

Testing

• make test
• Build the docker image, run the main.py in the container, and verified makrdown/csv files are generated as expected.

[bluesentinelsec]

This is much improved, thanks!