Set mistral-server workers using openstack_service_workers

Change-Id: Ic5511cb4551a92f1ef7d2d830678d9629b0f0f1f
Closes-Bug: #1671759

ansible/roles/mistral/templates/mistral.conf.j2

@@ -13,6 +13,7 @@ transport_url = rabbit://{% for host in groups['rabbitmq'] %}{{ rabbitmq_user }}
 [api]
 host = {{ hostvars[inventory_hostname]['ansible_' + api_interface]['ipv4']['address'] }}
 port = {{ mistral_api_port }}
+api_workers = {{ openstack_service_workers }}
 {% endif %}
 
 [database]