Disable re-execute in buildroot for Commit Queue.
Disable re-execute in buildroot for Commit Queue.

Right now there's a bug related to maintaining state in the Commit Queue when
we re-execute from the buildroot. We should disable the re-execution until that
is resolved.

BUG=chromium-os:23814
TEST=Test commit queue and preflight queue runs. pylint + unittests. Verify
     preflight still re-executes, but commit queue does not.

Change-Id: I17886777fcfcea37985183364f973836a38fbca8
Reviewed-on: https://gerrit.chromium.org/gerrit/12495
Tested-by: David James <f231dc574bbeb62604660cbc162d1b8642a0a3af@chromium.org>
Reviewed-by: David James <f231dc574bbeb62604660cbc162d1b8642a0a3af@chromium.org>

bpsinc-native/src_third_party_chromite,zhang0137/chromite,bpsinc-native/src_third_party_chromite,chadversary/chromiumos.chromite,chadversary/chromiumos.chromite,zhang0137/chromite,coreos/chromite,coreos/chromite,coreos/chromite,zhang0137/chromite,bpsinc-native/src_third_party_chromite