shill: rename _unittest.* to _test.* This matches the Google style guide and our linter. BUG=None TEST=precq passes Change-Id: Ibf9ad0fb83f77ec6b2148dd2a0b71e69c9155fda Reviewed-on: https://chromium-review.googlesource.com/1195585 Commit-Ready: Ben Chan <benchan@chromium.org> Tested-by: Ben Chan <benchan@chromium.org> Reviewed-by: Mike Frysinger <vapier@chromium.org>