Move VbNvContext setup/teardown to vboot wrapper funcs

BUG=chromium-os:18226
TEST=make && make runtests

Change-Id: Ie22e99a9796866e646ed92158410bc7a2fdf90f6
Reviewed-on: http://gerrit.chromium.org/gerrit/4754
Reviewed-by: Stefan Reinauer <reinauer@google.com>
Tested-by: Randall Spangler <rspangler@chromium.org>
7 files changed