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