Hub programmer needs to set port voltage

[aacuevas]

Starting with onix firmware 2.0, hubs are shut down automatically when context closes, so there is no persistence of power state. As such, the hub updater needs to power up the ports and issuing a refresh before attempting an update.

@jonnew Should the voltage be an option? Should it have a default or be a mandatory option?

[jonnew]

I think the voltage should be an option for now, along with #8 for a truly automated solution. I will amend #7 to allow this.