factory_install: Detect virtual developer switches.

"crossystem vdat_flags" is the better & portable way to find out developer
switch state.

BUG=chromium-os:32836
TEST=Manual.

Change-Id: I38f4b5bc590e59b1bedb5aa919479e3f09e90e36
Reviewed-on: https://gerrit.chromium.org/gerrit/28480
Commit-Ready: Hung-Te Lin <hungte@chromium.org>
Tested-by: Hung-Te Lin <hungte@chromium.org>
Reviewed-by: Jay Kim <yongjaek@chromium.org>
1 file changed