Implement ZK anti-affinity

We want the zk servers spread out across all nodes of the cluster,
both to level out memory usage and for fault tolerance.

Change-Id: I31e3115a046147a77c54cfa84765fe73334888b5

k8s/zookeeper/zookeeper.yaml

diff --git a/k8s/zookeeper/zookeeper.yaml b/k8s/zookeeper/zookeeper.yaml
index 91e42a5..72538f6 100644
--- a/k8s/zookeeper/zookeeper.yaml
+++ b/k8s/zookeeper/zookeeper.yaml
@@ -251,8 +251,17 @@
       securityContext:
         fsGroup: 1000
         runAsUser: 1000
+      affinity:
+        podAntiAffinity:
+          requiredDuringSchedulingIgnoredDuringExecution:
+            - labelSelector:
+                matchExpressions:
+                  - key: "app"
+                    operator: In
+                    values:
+                      - zookeeper
+              topologyKey: "kubernetes.io/hostname"
       containers:
-
         - name: zookeeper
           image: "zookeeper:3.7.1"
           imagePullPolicy: IfNotPresent