Add --kubernetes flag and run model in outdir when outdir is local

[mcgibbon]

Major changes:

• Added --kubernetes command-line flag to output a kubernetes config yaml to stdout
• When output location is set to a local path, the job now runs in that output location instead of in a temporary directory which then gets copied. This is done both to reduce copying time for large jobs, and to improve visibility of model behavior while running.

Minor changes:

• Updated filesystem.is_local_path naming to be package-private instead of module-private
• Fixed an issue where the subprocess-wrapped run_native lived inside an imported module, resulting in python warnings

[oliverwm1]

LGTM. Can you add the --kubernetes option to the docs?

Is there a plan to allow more precise specification of Kubernetes resources from the command line? The feature as it currently stands seems of somewhat limited utility if it only allows runs with cpu_count=1 and memory_gb=3.6GB, the current defaults for run_kubernetes.

[nbren12]

@oliverwm1 I think it would be fair for the fv3run CLI to support all the current parameters of run_kuberenetes. That said, @mcgibbon and I are concerned that adding more features to functions like run_kuberentes (e.g. volume mounts etc) could result in a function with so many arguments that it basically equivalent to a k8s yaml. At that point, I think we should just write raw K8s jobs as yaml files, templates for which could be generated with run_k8s.

[mcgibbon]

After discussing with @oliverwm1 and @nbren12 I'm modifying this so --kubernetes will output the job yml to stdout instead. Will get in touch when it's ready for re-review.