[MAINTENANCE] Make helm_install_namespace default value "cnf-default"

[barmull]

• remove helm_install_namespace from all samples except coredns samples
• cnfs are deployed into cnf-default namespace
• add condition into cleanup to terminate pods from cnf-default namespace
• update ## helm_install_namespaces section in CNF_TESTSUITE_YML_USAGE.md file

Description

The best practice is not installing CNF to the default namespace on cluster.

Issues:

Refs: #2039

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
  • [X] Kind cluster
• [ ] Have not tested

Types of changes:

• [ ] Bug fix (non-breaking change which fixes an issue)
• [x] 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

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

Code Review

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

Issue

• [ ] Tasks in issue are checked off

[horecoli]

LGTM