Filter out some Clover coverage to prevent false positives
Summary: Clover reports generated from PHPUnit sometimes give false positives of lines that were not covered by a test that should have actually been not coverable, apparently due to inaccurate static analysis of files that weren't actually executed. This filters coverage reports of files that show no coverage which avoids these false positives. Fixes T10420.
Looked at coverage reports of files before and after the change
Reviewers: Blessed Reviewers, epriestley
Reviewed By: Blessed Reviewers, epriestley
Subscribers: Korvin, aurelijus
Maniphest Tasks: T10420
Differential Revision: https://secure.phabricator.com/D15343