We added the ability to filter the ingresses used by traefik based
on a label selector, but we shouldn't need to have matching
labels on every other resource, Ingress allready has a way
to explicty choose which pods end up in the load ballancer
(by refering to the membership of a particular service)
Since we already know the name and namespace
of the service(s) we want we can just get the
correct one back from the API without filtering
the results.
* Potentialy saves a network hop
* Ability to configure LB algothim (given some work to expose an
anotation etc...)
* K8s config Watch is triggered far less often
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
