test.py: compute coverage per top-level module.

infra/.coveragerc

 [run]
-include = ./*
+include = ./infra/*
 omit =
-    # Virtual environment with third_party packages.
-    ./ENV/*
-
-    # Add chromium_build, which wasn't test.py-enabled for a long time.
-    ./appengine/chromium_build/*
-
-    # Add monorail's third-party packages and worst offenders
-    ./appengine/monorail/third_party/*
-    ./appengine/monorail/testing/*
-
-    # Appengine third_party packages, committed into the repo as is.
-    ./appengine/third_party/*
-
-    # Luci code added via DEPS.
-    ./luci/*
-
     # Antibody third_party files
     ./infra/tools/antibody/static/third_party/*
 
 [report]
 exclude_lines =
     # Have to re-enable the standard pragma
     pragma: no cover
 
     # Don't complain about missing debug-only code:
     def __repr__
     if self\.debug
 
     # Don't complain if tests don't hit defensive assertion code:
     raise AssertionError
     raise NotImplementedError
 
     # Don't complain if non-runnable code isn't run:
     if 0:
     if __name__ == ['"]__main__['"]:
 
 [expect_tests]
-expected_coverage_min = 92
+expected_coverage_min = 100