Kill _all_ builders when a build fails
Kill _all_ builders when a build fails

Currently builders that shouldn't cause the others to be killed aren't
killed themselves either when one of the gated builders fails. That
doesn't seem right.

rust-lang/rust-buildbot,rust-lang/rust-buildbot,aidanhs/rust-buildbot,aidanhs/rust-buildbot,edunham/rust-buildbot,rust-lang-deprecated/rust-buildbot,edunham/rust-buildbot,rust-lang/rust-buildbot,rust-lang-deprecated/rust-buildbot,aidanhs/rust-buildbot,edunham/rust-buildbot,rust-lang-deprecated/rust-buildbot