Support --buid-arg for upstream repos

[alexlovelltroy]

This PR alone will not fully address issue #2. More work is needed to make the liveness python library available externally and to then deprecate the --index-url flags from the requirements.txt files. It's a start though. Use build args like:

docker build -t cfs-operator-test --build-arg BASE_CONTAINER=alpine:3.12.0 --build-arg PIP_INDEX_URL=https://pypi.python.org/simple/ -f Dockerfile .

Keep in mind that in Dockerfiles the ARGS are cleared at each FROM line which is why they are defined multiple times in the same file.

[rkleinman-hpe]

What needs to happen for #2 (specifically the python package) to be available externally?

[alexlovelltroy]

I think we need to publish k8s-liveness to pypi or flip the repo to public and reference the github repo in requirements.txt

[rkleinman-hpe]

I vote for the latter, should be simple to do.

[alexlovelltroy]

I'd like @tpletcher-hpe to weigh in about referencing a github repo in requirements.txt and how he feels about the software supply chain on that.

[rkleinman-hpe]

It will be problematic or will require some build time tooling to switch between referencing the github repo vs the internal repo until we have just one repo to rule them all.

[rkleinman-hpe]

I have incorporated the changes for this into another PR that has now been merged internally, commit 8eec44b should have everything and will likely create a conflict with this PR. Suggest closing.

[rkleinman-hpe]

Changes have been incorporated on the HPE side. Closing.