Call docker-args plugins before running containers

The reason for this is that I connect to both MySQL & Docker via a socket which I mount using a volume, so I set the following docker args:

```
-v /var/run/mysqld/mysqld.sock:/var/run/mysqld/mysqld.sock
-v /var/run/docker.sock:/var/run/docker.sock
```

My pre deploy tasks (one being `rake db:migrate`) need these args to be able to run.