add support for environment variables in device tests

Previously device tests included information such as access point SSID/password at compile time. This made it difficult to compile test binaries once and then send them to multiple test runners for execution.

This change adds a command to the test library to set environment variable on the target device: “setenv key value”. C library setenv/getenv facility is used to store variables.

Test runner, tests, and makefile are updated to use this functionality.

tests/device/test_schedule/test_schedule.ino

@@ -1,5 +1,4 @@
 #include <BSTest.h>
-#include <test_config.h>
 #include <Schedule.h>
 
 BS_ENV_DECLARE();