Convert `vulnscan.py` to use the `pyTenable` package for Nessus connectivity

[mcdonnnj]

🚀 Feature Proposal

Change the vulnscan.py job to use the pyTenable package for interfacing with the Nessus API.

Motivation

Leveraging a package to handle interfacing with the Nessus API would be beneficial for the following reasons:

• We would be able to eliminate the custom written NessusController class from both the vulnscan.py job and nessus_base.py file used to configure Nessus when an instance is spun up.
• We could more easily implement testing with the test_nessus.py file as it would no longer rely on the vulnscan.py job.

Pitch

Having the pyTenable package pre-installed wherever jobs are run would be a simple addition to cisagov/ansible-role-cyhy-runner as we have already added PyYAML to support retrieving Nessus access information from a file. Eliminating the NessusController class will also allow easier maintenance of any jobs that relied on it and ensure that anything that interacts with Nessus does so in a consistent manner. With this change we can also rope test_nessus.py into getting updated so we have a straightforward file to test that Nessus works without relying on running a job through it from the commander.

[mcdonnnj]

Revisiting this we may want to look at using the pyTenable package (specifically the tenable.nessus sub-package) for the core connectivity to Nessus Professional.