first pass at adding 'stable' and 'edge' version packages

- Only have ubuntu to test on
  - fedora and redhat are placeholders/guesses
  - the "old" package repositories seem to have the "new" CE version which is `1.13.1` based
- `docker-ce` looks like it is named as a backported `docker-engine` package in some
  places

- Did not change the `defaults` version anywhere, so should work as before
- Did not point to new package repositories, as existing ones have the new packages.

roles/docker/vars/fedora.yml

@@ -1,9 +1,15 @@
 docker_kernel_min_version: '0'
 
+# https://docs.docker.com/engine/installation/linux/fedora/#install-from-a-package
+# https://download.docker.com/linux/fedora/7/x86_64/stable/
+# the package names below are guesses;
+# docs mention `sudo dnf config-manager --enable docker-ce-edge` for edge
 docker_versioned_pkg:
   'latest': docker
   '1.11': docker-1:1.11.2
   '1.12': docker-1:1.12.5
+  'stable': docker-ce
+  'edge': docker-ce-edge
 
 docker_package_info:
   pkg_mgr: dnf