Fix two issues in owners worker

Summary:
Fix two issues in PhabricatorRepositoryCommitOwnersWorker:

• if a commit was reviewed by some owner of the package, it should not be marked as needing audit
• do not run herald worker when it is not needed (for example, when the worker is executed from reparse.php)

Test Plan:
reparse a commit which is reviewed by the owner of a package
and verify that it is not marked as needing audit, and herald is not
executed.

Reviewers: nh, epriestley

Reviewed By: epriestley

CC: aran, epriestley

Differential Revision: https://secure.phabricator.com/D1496