fix nginx-tcp-and-udp on same port

[lkirill]

In nginx-ingress-controller if using

        - --udp-services-configmap=$(POD_NAMESPACE)/nginx-ingress-udp
        - --tcp-services-configmap=$(POD_NAMESPACE)/nginx-ingress-tcp

configs with same port, 53 for kube-dns as example:

apiVersion: v1
kind: ConfigMap
metadata:
  name: nginx-ingress-udp
data:
  53: "kube-system/kube-dns:53"

and

apiVersion: v1
kind: ConfigMap
metadata:
  name: nginx-ingress-tcp
data:
  53: "kube-system/kube-dns:53"

in nginx.conf will be created two upstreams with same name:

upstream kube-system-kube-dns-53 {...}

and nginx failing to start

[k8s-reviewable]

This change is 

[aledbf]

/lgtm

[coveralls]

Coverage remained the same at 43.178% when pulling 23c4534 on lkirill:nginx-udp-and-udp-fix into 4f04537 on kubernetes:master.

[aledbf]

@lkirill thanks!