SignerTestBuilder: Use PreCqBuilder base class.

I did some refactoring a while back to make it easier to add new PreCQ
builders. I didn't adjust the SignerTestBuilder to use it until the
new mechanism was proven out. However, while creating the new
mechanism I modified GenericBuilder in a way that broke
SignerTestBuilder.

BUG=chromium:706257
TEST=run_tests

Change-Id: Ibf5b5bbd8f7a378e2a5e8b71f6ff01ec47f905bc
Reviewed-on: https://chromium-review.googlesource.com/465353
Commit-Ready: Don Garrett <dgarrett@chromium.org>
Tested-by: Don Garrett <dgarrett@chromium.org>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
1 file changed