Autofocusing on all cameras doesn't start simultaneously

[Physarah]

By the time jetson8 starts auto focusing, jetson0 has reached position 3/4. The same happens with flats

[danjampro]

This is because supposedly asynchronous calls to take_exposure and autofocus_cameras do not return immediately. The best solution is a redesign of the base code in POCS. In the mean time we could think about writing an asynchronous dispatcher, which would call e.g. take_exposure in a thread pool and return the corresponding events.