Add support for setting test shell variables in device dictionary
This patch adds the field "environment" to the device dictionary, containing device-specific shell variables which will be available in the LAVA test shell.
These can be used, for example, to describe physical hardware connections between the DUT and interfaces on the worker or other addressable hardware.
Closes #228 (closed).
Signed-off-by: Tim Jaacks firstname.lastname@example.org