Running Python2 and Python3 tests seperately
The list of available tests in the run-tests.sh help specifies sdk/python and sdk/python:py3 separately. Using sdk/python:py3 actually doesn't run any tests. Instead, using sdk/python runs the tests twice (once against py2 and once against py3).
We should either support running them separately or remove sdk/python:py3 from the help list. If we decide to support running them separately, make sure to add sdk/cwl:py3 to the help list also.