support/run-tests: reorder imports

Reorder imports using the isort utility to fix a warning from pylint3:

wrong-import-order: standard import "import multiprocessing" should be
placed before "import nose2"

Signed-off-by: Yegor Yefremov <yegorslists@googlemail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>