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

This allows specifying minimum expected coverage per python module.

BUG=606878
R=pgervais@chromium.org

Review-Url: https://codereview.chromium.org/1917383002
Cr-Mirrored-From: https://chromium.googlesource.com/infra/infra
Cr-Mirrored-Commit: 0e47fe74a32e0030ba927470c4df050907d626ce
1 file changed