Docker login (#894)

* Add docker_login rule

* Add docker_login rule

* Whitespace fix

* Fix typo in test case

* Fix typo in test case

* Add test cases

README.md

@@ -190,6 +190,7 @@ following rules are enabled by default:
 * `dirty_unzip` – fixes `unzip` command that unzipped in the current directory;
 * `django_south_ghost` – adds `--delete-ghost-migrations` to failed because ghosts django south migration;
 * `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`;
 * `dry` – fixes repetitions like `git git push`;
 * `fab_command_not_found` – fix misspelled fabric commands;