Add test config to net_test_device

This change allows TradeFederation to run the test directly.
Refer to b/35882476 for design and discussion of this change.

Bug: 35882476
Test: local test
tradefed.sh run template/local --template:map test=net_test_device

Change-Id: Ie3e287aba9cd38cbfceef36885c863ba2d34b31a