Consider allowing switching DUT voltage in classes that don't inherit DeviceInteractor directly

[acostach]

It might be useful to allow overriding DUT voltage for classes that don't inherit DeviceInteractor directly, for use-cases like this:

class SDFlasher extends DeviceInteractor class BeagleBone extends SDFlasher

where only SDFlasher can set the readonly variable powerVoltage of DeviceInteractor.