This allows requesting environment variable values set in the C++ test
code, from python mock code. Use case is cross-checking test
results against values expected by the host side part of the test.
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.