unify vboot path vars

A bunch of scripts duplicate vboot paths, so unify them all in common.sh.

BUG=chromium:660209
TEST=precq passes

Change-Id: I7e568a205a0ab93ed6a413a88f9bb79c06095883
Reviewed-on: https://chromium-review.googlesource.com/427498
Commit-Ready: Mike Frysinger <vapier@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
Reviewed-by: David Riley <davidriley@chromium.org>
8 files changed