Update imagePullPolicy for unstable images

- Update imagePullPolicy from IfNotPresent to Always
  for all unstable images we are using in k8s template,
  because those images are updated regularly, we will
  keep it unstable until the official release.
- Use Tendermint v0.13 as base docker image, since our current
  integration is based out of v0.13

k8s/nginx-https/nginx-https-dep.yaml

@@ -13,7 +13,7 @@ spec:
       containers:
       - name: nginx
         image: bigchaindb/nginx_https:unstable
-        imagePullPolicy: IfNotPresent
+        imagePullPolicy: Always
         env:
         - name: CLUSTER_FRONTEND_PORT
           valueFrom: