Look at child tracebacks when deciding what CLs to submit.
Look at child tracebacks when deciding what CLs to submit.

Currently the master buildbot just looks at its own tracebacks when
deciding what CLs to submit. Don't do that -- look at the child builders
instead.

BUG=chromium:310671
TEST=Run x86-mario-paladin buildbot run. Unit tests.

Change-Id: I88d5989294deac1dd858b1fe4d79d8a3b3ff34c4
Reviewed-on: https://chromium-review.googlesource.com/175400
Reviewed-by: David James <f231dc574bbeb62604660cbc162d1b8642a0a3af@chromium.org>
Tested-by: David James <f231dc574bbeb62604660cbc162d1b8642a0a3af@chromium.org>

bpsinc-native/src_third_party_chromite,chadversary/chromiumos.chromite,bpsinc-native/src_third_party_chromite,bpsinc-native/src_third_party_chromite,chadversary/chromiumos.chromite