Merge pull request #377 from tseaver/fail-coverage_lt_100_pct

Fail if coverage < 100%.
Revert "Fail if coverage < 100%."
Merge pull request #378 from GoogleCloudPlatform/revert-377-fail-coverage_lt_100_pct

Revert "Fail if coverage < 100%."
Revert "Revert "Fail if coverage < 100%.""

This reverts commit 8db38b75e7560f8c7b5b710c51e3c299578970ca.