Use eatmydata with zookeeper in tests

This uses eatmydata with zookeeper when we run our tests.  This
should allow us to avoid using a tmpfs (which uses memory) for
ZK, which generally shouldn't need to read back any data in our
unit tests, so we don't really care how long background writes
take.  This should save 3/4 of a GB of ram.

Change-Id: I64ef1e9028d836c91d1c7c59909ac1f5a54db2a5

playbooks/zuul-nox/pre.yaml

@@ -1,7 +1,29 @@
 - hosts: all
+  name: Prepare node for Zuul tests
   roles:
     - configure-swap
     - ensure-dstat-graph
     - run-dstat
     - role: ensure-zookeeper
       zookeeper_use_tls: true
+      zookeeper_use_tmpfs: false
+
+- hosts: all
+  name: Use eatmydata with ZooKeeper
+  tasks:
+    - name: Install eatmydata
+      package:
+        name: eatmydata
+        state: present
+      become: true
+    - name: Ensure Zookeeper is not running
+      command: pkill -f zookeeper
+      register: _pkill
+      # 0 is killed
+      # 1 is no process matched
+      # >1 is some sort of actual error
+      failed_when: _pkill.rc > 1
+      become: true
+    - name: Start Zookeeper
+      command: eatmydata /opt/zookeeper/bin/zkServer.sh start
+      become: true