`coverage run pytest` runs coverage against the tests in a file called
"pytest", whereas `coverage run -m pytest` uses pytest as the test
runner, which is what we really want here.
To avoid duplicated maitenance of pytest arguments,
unit_tests.sh is updated to handle the coverage run.
Co-Authored-By: Akihiro Motoki <amotoki@gmail.com>
Change-Id: I106cb5227ca8c4f0a6f9d81c37e745a6f304de45
1202faa709