Add support for Go 1.10 (cached) output

Summary:
In Go 1.10 the output for tests was changed to have also a "(cached)" mode in
addition to the normal timing info printed. This is on by default. This adds
support for parsing these lines instead of erroring out on the regex.

Test Plan: Have a unit test included, and will continue to poke at it locally.

Reviewers: epriestley, Blessed Reviewers

Reviewed By: epriestley, Blessed Reviewers

Subscribers: Korvin

Differential Revision: https://secure.phabricator.com/D19161