By design k8s ingress is only designed to ballance services from within
the namespace of the ingress.
This is disscuessed a little in
https://github.com/kubernetes/kubernetes/issues/17088.
For now traefik should only reference the services in the current
namespace. For me this was a confusing change of behaviour
from the reference implimentations, as I have services
with the same name in each namespace.
If the flag kubernetes.namespaces is set...
Then we only select ingresses from that/those namespace(s)
This allows multiple instances of traefik to
independently load balance for each namespace.
This could be for logical or security reasons.
Addresses #336
