Docker remove container before remove image (#928)

* add docker container removal

* remove container before deleting image

* update readme

* clean up and add assert not test

* test not docker command

* use shell.and_ correctly

README.md

@@ -191,6 +191,7 @@ following rules are enabled by default:
 * `django_south_merge` – adds `--merge` to inconsistent django south migration;
 * `docker_login` – executes a `docker login` and repeats the previous command;
 * `docker_not_command` – fixes wrong docker commands like `docker tags`;
+* `docker_image_being_used_by_container` ‐ removes the container that is using the image before removing the image;
 * `dry` – fixes repetitions like `git git push`;
 * `fab_command_not_found` – fix misspelled fabric commands;
 * `fix_alt_space` – replaces Alt+Space with Space character;