We have been running into what appear to be zookeeper performance issues
causing tests to fail. Run the zookeeper on a tmpfs to reduce the impact
of iops to disk.
Other alternatives include using something like eatmydata to make writes
and syncs fast but unsafe.
Change-Id: Iea5e44af6844281c7f2078da57da9f13691e2642
674d6d88b4