TRON-2195: Support watcher_kubeconfig_paths

[jfongatyelp]

Requires Yelp/task_processing#213 & new version of taskproc to be released.

This adds the support to tron's MASTER config's k8s_options to allow the new old_kubeconfig_paths option and passes it along to task_processing's kubernetes_pod_executor.

[cuza]

don't we need to add validation and a default value for this in tron/config/config_parse.py? Something like:

class ValidateKubernetes(Validator):
    config_class = ConfigKubernetes
    optional = True
    defaults = {
        "kubeconfig_path": None,
        "old_kubeconfig_paths": None
        "enabled": False,
        "default_volumes": (),
    }

    validators = {
        "kubeconfig_path": valid_string,
        "old_kubeconfig_paths": valid_string
        "enabled": valid_bool,
        "default_volumes": build_list_of_type_validator(valid_volume, allow_empty=True),
    }

[jfongatyelp]

don't we need to add validation and a default value for this in tron/config/config_parse.py?

Thanks! That's probably a good call to maintain parity w/ all the rest of our configs + validate values for watcher_kubeconfig_paths. That said I've always been a bit confused why we specify defaults both in config_parse and in the schema classes themselves. Currently this still works fine w/o errors (verified on one of our test tron servers w/ setting + unsetting watcher_kubeconfig_paths and updating via paasta_setup_tron_namespace) since we are just using the ConfigKubernetes schema class (which I've updated in this PR) in config_parse, and so it gets the default I've specified there.