Add event flags to build_packages

* Added --withevents flag to enable events in parallel_emerge
* Added --eventdir flag that is passed through to parallel_emerge

BUG=chromium:660050
TEST=./build_packages --withevents --board "x86-generic"
CQ-DEPEND=CL:413424

Change-Id: I081392bd7bc8d05bee7f9aac120a24e396abdb4b
Reviewed-on: https://chromium-review.googlesource.com/413155
Commit-Ready: Douglas Anderson <dianders@chromium.org>
Tested-by: Chris Ching <chingcodes@chromium.org>
Reviewed-by: Aviv Keshet <akeshet@chromium.org>
2 files changed