Add option to prefix log message with thread ID or thread name.
Align tests and add test case to the log_output test.
Signed-off-by: Krzysztof Chruściński <krzysztof.chruscinski@nordicsemi.no>
Adds tests for the custom timestamp functionality. It also
includes a basic test for the default behaviour.
Signed-off-by: Hein Wessels <heinwessels93@gmail.com>