run_tests.py: Make it possible to select specific test sets to run

Signed-off-by: Jerome Flesch <jflesch@gmail.com>
Tests: RawApi: fix test_get_option_descriptor_0():
the first option (which has for value the number of options available) don't always have the same name, depending on the backend

Signed-off-by: Jerome Flesch <jflesch@gmail.com>