ev3 (only!): enable power off

This makes it possible to use the usual commands like halt -p or poweroff
to power down the LEGO EV3 brick.

Signed-off-by: Alexander Holler <holler@ahsoftware.de>
Merge pull request #22 from aholler/master

ev3 (only!): enable power off
lms2012: exit-script: use poweroff to power off the EV3

Now that poweroff does work, use it.
d_power: Disable power off when module is unloaded

Remove that violent piece of code which does look like if someone
hits a mechanical button over and over in order to make it work.
We live in the digital age.
Merge pull request #23 from aholler/master

power off finalized