Pass arbitrary params to the watching GET queries

[nolar]

GET queries of K8s API can accept some params, which are especially needed for the watching GET-queries. These params are NOT the request body and not the payload, but the execution modes/flags.

For example, for pod-watching: https://kubernetes.io/docs/reference/generated/kubernetes-api/v1.10/#watch-64

The set of these params can change over time. To avoid mapping each and every one of them to pykube's codebase (and resolving the camelCase conventions to Python's snake_case), this PR adds params option to watch() call — and passes them directly to the query params.

For example, this script disables the socket timeouts, but asks the server to limit the query to 10s (server-side!). When the time runs out, the query ends normally, without any exceptions.

import pykube

cfg = pykube.KubeConfig.from_file()
api = pykube.HTTPClient(cfg, timeout=None)
stream = pykube.Pod.objects(api).watch(params=dict(timeoutSeconds=10))

for event in stream:
    print(repr(event))

Whether or not such params should be added to other operations (e.g. listing), is a question to discuss. Most of the writing operations (patch, create, replace) only have pretty param, which is useless; however, delete has gracePeriodSeconds and propagationPolicy, which can be of use.

Issue: related #32

[hjacobs]

Thanks!