Pin docker version on RedHat and CentOS to the desired version

roles/docker/vars/redhat.yml

 docker_kernel_min_version: '0'
 
+# https://yum.dockerproject.org/repo/main/centos/7/Packages/
+# or do 'yum --showduplicates list docker-engine'
+docker_versioned_pkg:
+  'latest': docker-engine
+  '1.11': docker-engine-1.11.2-1.el7.centos
+  '1.12': docker-engine-1.12.6-1.el7.centos
+  '1.13': docker-engine-1.13.0-1.el7.centos
+
 docker_package_info:
   pkg_mgr: yum
   pkgs:
-    - name: docker-engine
+    - name: "{{ docker_versioned_pkg[docker_version | string] }}"
 
 docker_repo_key_info:
   pkg_key: ''