Twistlock parser fix for riskFactors + cve field

[madchap]

Got bitten by it today. This fixes it.

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.
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• Add applicable tests to the unit tests.

[madchap]

This PR supercedes #1117 (includes the cve too).

cc @dr3dd589 can you then maybe close your PR?

[valentijnscholten]

If the risk factors are not present in the import, does it mean there are no risk factors. Or does it mean there are no risk factors specified. Might sound like nitpicking, but just check to see if we want to change the default text to "No risk factors specified' :-)

[madchap]

@valentijnscholten good point. I'll keep that in mind when looking at these reports in the near future and amend as necessary 👍 (it should not block the merge though! ;-))