Import Debian changes 3.4.9-3+deb9u1

zookeeper (3.4.9-3+deb9u1) stretch-security; urgency=high

  * Team upload.
  * Fix CVE-2018-8012:
    No authentication/authorization is enforced when a server attempts to join
    a quorum in Apache ZooKeeper. As a result an arbitrary end point could join
    the cluster and begin propagating counterfeit changes to the leader.
    (Closes: #899332)