tinytest-codegen.py

The way tinytest was used in qemu-arm test target is that it didn't test
much. MicroPython tests are based on matching the test output against
reference output, but qemu-arm's implementation didn't do that, it
effectively tested just that there was no exception during test
execution. "upytesthelper" wrapper was introduce to fix it, and so
test generator is now switched to generate test code for it.

Also, fix PEP8 and other codestyle issues.