assumes abs path to ca

[jason-kane]

    kubernetes = network_kubernetes_from_context(reactor, context_name, config_path)
  File "/usr/local/lib/python2.7/dist-packages/txkube/_network.py", line 80, in network_kubernetes_from_context
    cluster = config.clusters[context[u"cluster"]]
  File "/usr/local/lib/python2.7/dist-packages/pykube/config.py", line 142, in clusters
    BytesOrFile.maybe_set(c, "certificate-authority")
  File "/usr/local/lib/python2.7/dist-packages/pykube/config.py", line 225, in maybe_set
    d[file_key] = cls(filename=d[file_key])
  File "/usr/local/lib/python2.7/dist-packages/pykube/config.py", line 241, in __init__
    raise exceptions.PyKubeError("'{}' file does not exist".format(filename))
pykube.exceptions.PyKubeError: 'dev-ca.crt' file does not exist``` 

```$ cat ~/.kube/config
apiVersion: v1
clusters:
- cluster:
    certificate-authority: dev-ca.crt
...

the ca file resides in ~/.kube/dev-ca.crt. The same problem reoccurs with users[].user.client-certificate and .client-key. Putting absolute paths into ~/.kube/config appears to avoid the issue.

[exarkun]

Thanks. It looks like this is a problem with pykube. I've forwarded the report upstream, we'll see what they say.