484 metrics port

[ryandawsonuk]

fixes #484

Checked this by adding parameters to helm install for seldon-core - --set engine.port=14040 --set engine.grpc.port=14041 --set engine.prometheus.path="micrometheus". Then installed a model and was able to validate that the pod spec contained:

kind: Pod
metadata:
  annotations:
    prometheus.io/path: /micrometheus
    prometheus.io/port: "14040"
    prometheus.io/scrape: "true"
...
    - name: ENGINE_SERVER_PORT
      value: "14040"
    - name: ENGINE_SERVER_GRPC_PORT
      value: "14041"
...
   ports:
    - containerPort: 14040
      protocol: TCP
    - containerPort: 14041
      name: grpc
      protocol: TCP

Also ran the E2E tests

[ukclivecox]

Looks good. This will effect the AWS marketplace release as the Helm chart has changed.