Improve onExit command handler when exit command runs

[FelipeBarrosCruz]

onExit key on global schema is a shell script to execute like handler on exit command like docker-compose stop or anything you want to.

Pull request on fuge-config:
apparatus/fuge-config#11

fuge_global:
  tail: false
  monitor: false
  monitor_excludes:
    - '**/node_modules/**'
    - '**/.git/**'
    - '**/*.log'
  onExit:
    docker-compose -f docker-compose.yml stop;

[pelger]

Nice one - thanks! I think that this could be generally useful. Couple of things before merge please:

• On fuge-config could you change the setting to be on_exit to be consistent with the rest of the config file.

• On fuge-config could you add a unit test for this setting - this could be just an update to an existing fixture just to ensure it is passed through correctly

• on this repo (fuge) could you add a unit test for on_exit

Let me know if you need any help doing this! Will merge once these are in.
Cheers.