Add flag to http client to allow for the client to be dryrun

[lukemassa]

This allows you to create an http client that will only make dry run requests. (https://kubernetes.io/blog/2019/01/14/apiserver-dry-run-and-kubectl-diff/)

>>> import pykube
>>> pod = {'apiVersion': 'v1', 'kind': 'Pod', 'metadata': {'name': 'lmassa-test', 'namespace': 'node-maintenance-api'}, 'spec': {'containers': [{'name': 'uname', 'image': 'alpine', 'command': ['sleep', '10000000']}]}}
>>> api_real = pykube.HTTPClient(pykube.KubeConfig.from_file("config"), dry_run=False)
>>> api_dryrun = pykube.HTTPClient(pykube.KubeConfig.from_file("config"), dry_run=True)
>>> 
>>> pykube.Pod(api_dryrun, pod).exists()
False
>>> pykube.Pod(api_dryrun, pod).create()
>>> pykube.Pod(api_dryrun, pod).exists()
False
>>> pykube.Pod(api_real, pod).create()
>>> pykube.Pod(api_real, pod).exists()
True

[lukemassa]

Looks like coverage dropped, I'll see if I can add a test

[hjacobs]

Thanks for the contribution!

[lukemassa]

Removing WIP now that I got tests passing

[hjacobs]

Thanks! Just one tiny request: can you change the keyword argument to dry_run? This would be more consistent with the Kubernetes parameter (camelCase "dryRun" -> snake_case "dry_run")

[lukemassa]

@hjacobs updated!