Add delay to k8s config so Alphas start after Zeros.

From this discussion:
https://discuss.dgraph.io/t/kubernetes-contrib-config-doesnt-work-with-minikube/3592

Author: danielmai

contrib/config/kubernetes/dgraph-ha.yaml

@@ -210,6 +210,10 @@ spec:
                   values:
                   - dgraph-alpha
               topologyKey: kubernetes.io/hostname
+      initContainers:
+        - name: init-alpha
+          image: busybox
+          command: ['sh', '-xc', 'echo "Wait for Zeros to start" && sleep 10']
       containers:
       - name: alpha
         image: dgraph/dgraph:latest