Bastion_test system

[o0Ignition0o]

Is your feature request related to a problem? Please describe.

In test settings, It might sometimes be unfortunate to have a SYSTEM that handles all of the bastion lifecycle, especially when we want to isolate tests.

Describe the solution you'd like
The idea would be to have a bastion_test module that would be local to a test, and provide its own init() start() stop() and block_until_stopped() functions, that wouldn't interfere with other tests.

WDYT?

[o0Ignition0o]

Closing this because I don't think it's required, as long as we spawn distinct groups and target distinct distributors.