Reload haproxy configuration when config changes

Add an Ansible handler to send a hangup signal through
docker-compose to the running haproxy daemon any time the task to
update its configuration fires.

Change-Id: I1946c1e7eaaa8a8e2209007b5d065dba952ec6e2

playbooks/roles/haproxy/handlers/main.yaml

@@ -0,0 +1,4 @@
+- name: Reload haproxy
+  shell:
+    cmd: docker-compose kill -s HUP haproxy
+    chdir: /etc/haproxy-docker/

playbooks/roles/haproxy/tasks/main.yaml

@@ -19,6 +19,7 @@
   template:
     src: haproxy.cfg.j2
     dest: /var/haproxy/etc/haproxy.cfg
+  notify: Reload haproxy
 - name: Install docker-compose
   package:
     name: