mystamps-app: use systemd module

The puzzle `399-f88baadc` from #399 has to be resolved: 

https://github.com/php-coder/mystamps/blob/ff255631214be2581b2cf1533bda2e68644e5e9c/vagrant/provisioning/roles/mystamps-app/handlers/main.yml#L3-L3

The puzzle was created by Slava Semushin on 12-Jan-19.