fix #942

currently implemented only vulnerability scan for openscap.

Please submit your pull requests to the 'dev' branch.

When submitting a pull request, please make sure you have completed the following checklist:

• Your code is flake8 compliant (DefectDojo's code isn't currently flake8 compliant, but we're trying to correct that.)
• If this is a new feature and not a bug fix, you've included the proper documentation in the ReadTheDocs documentation folder. https://github.com/DefectDojo/Documentation/tree/master/docs or provide feature documentation in the PR.
• Model changes should include the necessary migrations in the dojo/dd_migrations folder.
• Add applicable tests to the unit tests.