bisect-kit: support non-default DEPS file name

In gclient's recursedeps entries, DEPS filename could be configurable,
not always "DEPS". Recently one such entry was added to src-internal.

BUG=None
TEST=bisect_cr_localbuild_internal with branch after 3579

Change-Id: I5b850399b6dd7f0405ef6fee4abd5276cdac070f
Reviewed-on: https://chromium-review.googlesource.com/1297557
Commit-Ready: Kuang-che Wu <kcwu@chromium.org>
Tested-by: Kuang-che Wu <kcwu@chromium.org>
Reviewed-by: Chi-Ngai Wan <cnwan@google.com>
2 files changed