rename common.mk to build.mk

This is to avoid confusion with the canonical common.mk file that is
a CrOS build system.

BUG=chromium-os:33327
TEST=`cros_run_unit_tests --board x86-alex -p vboot_reference` still works

Change-Id: I4b6719d58a4a8ab44b62c23c0e2c45b154374958
Reviewed-on: https://gerrit.chromium.org/gerrit/29578
Reviewed-by: Randall Spangler <rspangler@chromium.org>
Commit-Ready: Mike Frysinger <vapier@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
4 files changed