Enforce to restart docker service on proxy change

It is not enough to reload daemon config to change the
environment variable of the docker process.

Change-Id: I68306e585c0eb046a0930a5f937dfbec8148fcef
diff --git a/docker/host.sls b/docker/host.sls
index dbd2cc0..3a6d1d4 100644
--- a/docker/host.sls
+++ b/docker/host.sls
@@ -48,6 +48,8 @@
   - makedirs: True
   - require_in:
     - service: docker_service
+  - watch_in:
+    - service: docker_service
 
 {% else %}