Onboarder incompatible with ARM

[mat7ias]

Currently, the onboarder won't run on a Raspberry Pi (ARM).

"-bash: ./onboarder: cannot execute binary file: Exec format error"

There was some community interest to try out Raiden on a Pi, could be beneficial to make the onboarder compatible to get testing quicker. Or even a Pi tutorial similar to with MicroRaiden.

[czepluch]

@mat7ias I moved your issue to here, since this is where the onboarder lives.