Allow drivers to signal an analysis retry
Allow drivers to signal an analysis retry

Summary:
This change also adds a DriverIO interface that is useful for
decoupling driver implementations.

Reviewers: #core_team, fromberger

Reviewed By: #core_team, fromberger

Subscribers: fromberger

Differential Revision: https://phabricator-dot-kythe-repo.appspot.com/D1268

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