test: exmaple pytest + labgrid test

Uses docker as the 'device' under test (all I had available)

Has a py_binary (pytest_exmaple.py) that launches pytest with the passed into LG_ENV variable and runs all tests available in the file

Uses a small sh_test target 'pytest_report' to parse the result of running pytest and propogate errors as well as the JUNIT XML file

Run with: bazelisk test docker_test:pytest_report