Add Jaeger support for Adservice. (#111)

This is the first service that exports to jaeger. Others to follow.
Requires jaeger to be instantiated using 

- helm install --name jaeger stable/jaeger-operator
- kubectl apply -f jaeger.yaml

=== jaeger.yaml Content ===
apiVersion: io.jaegertracing/v1alpha1
kind: Jaeger
metadata:
  name: jaeger

Above steps will be added to README in subsequent PR.

kubernetes-manifests/adservice.yaml

@@ -31,6 +31,8 @@ spec:
         env:
         - name: PORT
           value: "9555"
+        - name: JAEGER_ENABLED
+          value: "false"
         resources:
           requests:
             cpu: 200m