This merges all test specs into one master-independent
builders.pyl file, which will unblock deprecating the master name as
a property on infra side.

Bug: chromium:830557
Change-Id: I0592505e77ede725ed43a26cabfd057bb0b911bd
Reviewed-on: https://chromium-review.googlesource.com/1046671Reviewed-by: Sergiy Byelozyorov <sergiyb@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#53017}