Combined the find_free_k8s_nodeport and find_free_port functions…

[bieryAtFnal]

… into a single one that supports an optional range; promoted a few warnings to errors in set_connectivity_service_port.py

Description

This Pull Request builds on the changes in #603, and the target merge branch is mrigan/k8s_changes.

My sense is that providing a single find_free_port function is cleaner than providing separate ones for K8s and non-K8s uses.

And, it seemed that several of the warnings in the set_connectivity_service_port Python function should actually be errors since several of the conditions seemed quite likely to cause problems later (with inconsistent information in the configuration).

I tested these changes with the usual regression tests.

Type of change

• Documentation (non-breaking change that adds or improves the documentation)
• New feature or enhancement (non-breaking change which adds functionality)
• Optimization (non-breaking change that improves code/performance)
• Bug fix (non-breaking change which fixes an issue)
• Breaking change (whatever its nature)

Testing checklist

• Unit tests pass (e.g. dbt-build --unittest)
• Minimal system quicktest passes (pytest -s minimal_system_quick_test.py)
• Full set of integration tests pass (daqsystemtest_integtest_bundle.sh)
• Python tests pass if applicable (e.g. python -m pytest)
• Pre-commit hooks run successfully if applicable (e.g. pre-commit run --all-files)

Further checks

• Code is commented where needed, particularly in hard-to-understand areas
• Code style is correct (dbt-build --lint, and/or see https://dune-daq-sw.readthedocs.io/en/latest/packages/styleguide/)
• If applicable, new tests have been added or an issue has been opened to tackle that in the future.
  (Indicate issue here: # (issue))

[MRiganSUSX]

lgtm