Fix the device dictionary for BBB so that it only has necessary commands

Issue Background

Neil Williams pointed out that the poweron_command is a typo. But that command has been in the device dictionary for a long time

Issue description

I've now run a successful test with a device dictionary containing only
{% extends 'beaglebone-black.jinja2' %}
{% set connection_command = '/vagrant/scripts/connectBBB.sh 10.24.3.102 8020 root lavauser123' %}
which is a lot simpler!

Acceptance criteria

Further testing and an change to configure_lava.sh to remove the irrelevant commands