Switch docker to 1.13

- Remove variable dup for Ubuntu
- Update Docker to 1.13

roles/docker/defaults/main.yml

-docker_version: '1.12'
+docker_version: '1.13'
 
 docker_package_info:
   pkgs:

roles/docker/vars/ubuntu.yml

 ---
-docker_version: '1.12'
 docker_kernel_min_version: '3.10'
 
 # https://apt.dockerproject.org/repo/dists/ubuntu-xenial/main/filelist
@@ -7,7 +6,7 @@ docker_versioned_pkg:
   'latest': docker-engine
   '1.11': docker-engine=1.11.1-0~{{ ansible_distribution_release|lower }}
   '1.12': docker-engine=1.12.6-0~ubuntu-{{ ansible_distribution_release|lower }}
-  '1.13': docker-engine=1.13.0-0~ubuntu-{{ ansible_distribution_release|lower }}
+  '1.13': docker-engine=1.13.1-0~ubuntu-{{ ansible_distribution_release|lower }}
 
 docker_package_info:
   pkg_mgr: apt