Support launch of subservice

[wilfriedroset]

It is currently not possible to launch subservice

services:
    group:
        services:
            'svc1':
                actions:
                    start:
                        cmd: service one start
            'svc2':
                actions:
                    start:
                        cmd: service two start

milkcheck -c . -n foo group.svc2 status
[10:08:30] ERROR    - Undefined service [group.svc2]
milkcheck -c . -n foo svc2 status
[10:09:40] ERROR    - Undefined service [svc2]

It would be useful to be able to launch only subservices

[wilfriedroset]

duplicate #5 sorry.