fix(customizing-docker): stop docker first

Without this change people will get the following error:

```
# systemctl status docker-tcp.socket
docker-tcp.socket - Docker Socket for the API
   Loaded: loaded (/etc/systemd/system/docker-tcp.socket; enabled)
   Active: inactive (dead)
   Listen: [::]:4243 (Stream)

Apr 02 13:36:15 core-01 systemd[1]: Starting Docker Socket for the API.
Apr 02 13:36:15 core-01 systemd[1]: Socket service docker.service already active, refusing.
Apr 02 13:36:15 core-01 systemd[1]: Failed to listen on Docker Socket for the API.
```