Fixup apiserver proxy to be namespace aware

The apiserver was not setting a proper namespace value for a request.

curl -s --insecure -u vagrant:vagrant https://10.245.1.2/api/v1beta1/proxy/services/db | python -m json.tool | more{
    "apiVersion": "v1beta1",
    "code": 500,
    "creationTimestamp": null,
    "kind": "Status",
    "message": "Invalid request.  Unable to address and item without a namespace
on context",
    "status": "Failure"
}

The fix is to assume the default namespace, unless an alternative is provided in the query parameter of the URL.

Added a placeholder TODO for the namespaces.md spec to address path structures for this when we move to make the namespace part of the URL path.