enable proxy support on docker repository

roles/docker/tasks/main.yml

@@ -49,8 +49,8 @@
   when: (not ansible_os_family in ["CoreOS", "Container Linux by CoreOS"]) and (docker_repo_info.repos|length > 0)
 
 - name: Configure docker repository on RedHat/CentOS
-  copy:
-    src: "rh_docker.repo"
+  template:
+    src: "rh_docker.repo.j2"
     dest: "/etc/yum.repos.d/docker.repo"
   when: ansible_distribution in ["CentOS","RedHat"]
 

roles/docker/templates/rh_docker.repo.j2

@@ -4,3 +4,4 @@ baseurl=https://yum.dockerproject.org/repo/main/centos/7
 enabled=1
 gpgcheck=1
 gpgkey=https://yum.dockerproject.org/gpg
+{% if http_proxy %}proxy={{ http_proxy }}{% endif %}