Bump down etcd version for zun

Docker libkv [1] does not support etcd of version >=3.4,
as otherwise ErrInvalidJSON exception is raised. Since
docker cluster-store is deprecated and removed in 23.0.0,
support of etcd won't be fixed.

At the same time while zookeeper is also a supported driver,
it's usage causes docker to crash on attempt to use it.

So bumping etcd version down is the only solution at the
moment.

[1] https://github.com/docker/libkv

Needed-By: https://review.opendev.org/c/openstack/openstack-ansible-os_zun/+/880288
Change-Id: I9a13d836f7f266c54283125dc09d11feeea23d3e

playbooks/os-zun-install.yml

@@ -32,6 +32,10 @@
       vars:
         etcd_cluster_group: "zun_api"
         etcd_install_type: server
+        etcd_version: 3.3.27
+        etcd_download_checksum:
+          x86_64: 'sha256:f9058f93e2f40343fd0bbbfce39ddb8a7afd8b03be020b7decc040d897065ded'
+          aarch64: 'sha256:7230b769efef5ac60a856d755776076597da5082d7a5904ee33995f921df8d8d'
   tags:
     - zun-install
     - etcd-server