Add exclusion of init system from single process check

[horecoli]

Description

This change defines a list of specialized init systems as a constant and excludes it from the verification of a single process check. This PR depends on https://github.com/cnf-testsuite/k8s_kernel_introspection/pull/3 which has to be merge first.

Issues:

Refs: #2038

How has this been tested:

• [ ] Covered by existing integration testing
• [ ] Added integration testing to cover
• [ ] Verified all A/C passes
  • [ ] develop
  • [ ] master
  • [ ] tag/other branch
• [ ] Test environment
  • [ ] Shared Packet K8s cluster
  • [ ] New Packet K8s cluster
  • [ ] Kind cluster
• [ ] Have not tested

Types of changes:

• [x] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] Documentation update

Checklist:

Documentation

• [ ] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.
• [x] No updates required.

Code Review

• [ ] Does the test handle fatal exceptions, ie. rescue block

Issue

• [ ] Tasks in issue are checked off

[horecoli]

The PR mentioned in the description, along with this PR, works fine with the dump-init and tini specialized init systems. However, there is different behavior in the case of the v6 init system (s6-svscan), which is not a single process init system but produces quite a lot of processes. So the main question is whether this case conflicts with the best practice of having single processes inside a container. I believe this needs to be discussed. Here is a screenshot showing how this test is failing with a list of processes:

[martin-mat]

This needs discussion @taylor @wavell @Smitholi67

My opinion: It is OK to handle init process as an exception for single-process-type test/best practice. However, S6 init system itself does not follow single-process principle, so it is fine to have failing single-process check when S6 is used. And also for that, we should reconsider recommending S6 as a best-practice init system for containers.

[horecoli]

The PR - https://github.com/cnf-testsuite/k8s_kernel_introspection/pull/3 to k8s_kernel_introspection was merged and new tag was created. So this PR is ready to merge.