Set train-dev as the default tag for heat-container-agent

Based on the policy of heat-container-agent tag, now it's updated
as train-dev and as long as we release Train, it will be updated
with train-stable.

Change-Id: Iec43df292dbd6a7e7ee33a0d4b8670b653a7ebbd

doc/source/user/index.rst

@@ -1209,7 +1209,7 @@ _`heat_container_agent_tag`
   This label allows users to select `a specific heat_container_agent
   version, based on its container tag
   <https://hub.docker.com/r/openstackmagnum/heat-container-agent/tags/>`_.
-  Stein-default: stein-dev
+  Train-default: train-dev
 
 _`kube_dashboard_enabled`
   This label triggers the deployment of the kubernetes dashboard.

magnum/drivers/k8s_fedora_atomic_v1/templates/kubecluster.yaml

@@ -554,7 +554,7 @@ parameters:
   heat_container_agent_tag:
     type: string
     description: tag of the heat_container_agent system container
-    default: stein-dev
+    default: train-dev
 
   keystone_auth_enabled:
     type: boolean

playbooks/container-builder-vars.yaml

@@ -15,6 +15,6 @@ kubernetes_images:
 
 magnum_images:
   - name: heat-container-agent
-    tag: stein-dev
+    tag: train-dev
 
 helm_version: v2.12.3

releasenotes/notes/heat-container-agent-for-train-e63bc1559750fe9c.yaml

@@ -0,0 +1,4 @@
+---
+other:
+  - |
+    Now the heat-container-agent default tag for Train release is train-dev.