Test with host

This is the first step of supporting the `:host` option for the `start_system` helper. The helper already works in the tests. Still missing:

* Bringing host into well-defined state before the test
* Locking host
* Mechanism to distribute the required configuration

Unused block argument - `global_options`. If it's necessary, use `_` or `_global_options` as an argument name to indicate that it won't be used.<br>Unused block argument - `options`. If it's necessary, use `_` or `_options` as an argument name to indicate that it won't be used.