Add GBB flags for disabling software sync and defaulting to legacy boot

1) GBB flag to skip EC software sync, so EC will be untouched.  Needed
for EC development.

2) GBB flag to default to booting legacy at end of dev screen timeout.
Very handy for booting Ubuntu (or other OS).

Also added unit tests for the new flags.

BUG=chrome-os-partner:20111
BRANCH=none
TEST=make runtests

Change-Id: I9da87d87014881a1b1393b0b4a5acb921d080066
Signed-off-by: Randall Spangler <rspangler@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/58270
Reviewed-by: Bill Richardson <wfrichar@chromium.org>
5 files changed