keep consistent with style of others

TrivialFix
It should be more comfortable to keep consistent:
$ find . -name *.yml | xargs grep -h -A5 start_container | grep name: | sort
    name: "ceph_mon"
    name: "ceph_rgw"
    name: "cinder_api"
    name: "cinder_backup"
    name: "cinder_scheduler"
    name: "cinder_volume"
    name: "glance_api"
    name: "glance_registry"
    name: "haproxy"
    name: "heat_api"
    name: "heat_api_cfn"
    name: "heat_engine"
    name: "horizon"
    name: "ironic-api"
    name: "ironic-conductor"
    name: "ironic-discoverd"
    name: "ironic-pxe"
    name: "keepalived"
    name: "keystone"
    name: "magnum_api"
    name: "magnum_conductor"
    name: "mariadb"
    name: "memcached"
    name: mistral_api
    name: mistral_engine
    name: mistral_executor
    name: "murano_api"
    name: "murano_engine"
    name: "neutron_agents"
    name: "neutron_openvswitch_agent"

Change-Id: Ie946286968c830dcc3c0c45cc9ba87418dd44e8c

ansible/roles/mistral/tasks/start.yml

@@ -2,7 +2,7 @@
 - name: Starting mistral-engine container
   kolla_docker:
     action: "start_container"
-    name: mistral_engine
+    name: "mistral_engine"
     common_options: "{{docker_common_options}}"
     image: "{{ mistral_engine_image_full }}"
     volumes:
@@ -13,7 +13,7 @@
 - name: Starting mistral-executor container
   kolla_docker:
     action: "start_container"
-    name: mistral_executor
+    name: "mistral_executor"
     common_options: "{{docker_common_options}}"
     image: "{{ mistral_executor_image_full }}"
     volumes:
@@ -24,7 +24,7 @@
 - name: Starting mistral-api container
   kolla_docker:
     action: "start_container"
-    name: mistral_api
+    name: "mistral_api"
     common_options: "{{docker_common_options}}"
     image: "{{ mistral_api_image_full }}"
     volumes: