tests/thread: Make stress_aes.py test run on bare-metal ports.
tests/thread: Make stress_aes.py test run on bare-metal ports.

This is a long-running test, so make it run in reasonable time on slower,
bare-metal ports.

Signed-off-by: Damien George <99e6b749acbfbe2a596df99e91d24d6e1fdbee00@micropython.org>

pfalcon/micropython,pfalcon/micropython,pfalcon/micropython,pfalcon/micropython,pfalcon/micropython