bisect-kit: fix bisect_cr_localbuild_master

1. two functions were missed in last commit.
2. fix starting rev when opts.old is chromeos or chrome version.

BUG=chromium:776314
TEST=manually performed a chrome master bisection

Change-Id: Ia1e23dc9ecc1ce86b4f1198738eb5879d14a8e5b
Reviewed-on: https://chromium-review.googlesource.com/896668
Commit-Ready: Kuang-che Wu <kcwu@chromium.org>
Tested-by: Kuang-che Wu <kcwu@chromium.org>
Reviewed-by: Owen Lin <owenlin@chromium.org>
3 files changed