Create three keystone containers when the test scenario includes 'keystone'

This patch makes the os_keystone role test create 3 keystone containers
to validate the ssh-keyspairs setup and sync of the fernet keys.

Change-Id: If51c2796a22b654c302b2a7d0941bc7bfc45760d

etc/openstack_deploy/openstack_user_config.yml.aio.j2

@@ -206,6 +206,17 @@ global_overrides:
           - manila_share
           - swift_proxy
 
+# keystone
+identity_hosts:
+  aio1:
+    ip: 172.29.236.100
+{% if 'keystone' in bootstrap_host_scenarios %}
+#   NOTE (jrosser) this ensures that we deploy 3 keystone containers
+#   during the os_keystone role test to validate ssh keys and fernet key sync
+    affinity:
+      keystone_container: 3
+{% endif %}
+
 # galera, memcache, rabbitmq, utility
 shared-infra_hosts:
   aio1: