Fix freezer elasticsearch config

storage settings for elasticsearch are not correct.
Need a backend and expecific options for the backend.

Change-Id: I71e35644389b6f97a20daf0f1dec29a30c3c34e3
Closes-Bug: #1713693

ansible/roles/freezer/templates/freezer-api.conf.j2

@@ -26,7 +26,10 @@ memcached_servers = {% for host in groups['memcached'] %}{{ hostvars[host]['ansi
 config_file = /etc/freezer/freezer-paste.ini
 
 [storage]
+backend = elasticv2
+driver = freezer_api.storage.elasticv2.ElasticSearchEngineV2
+
+[elasticv2]
 hosts = {{ internal_protocol }}://{{ kolla_internal_fqdn }}:{{ elasticsearch_port }}
 number_of_replicas = 0
 index = freezer
-db = elasticsearch