mount-encrypted: allow stateful mount check to pass factory install

When factory install happens, mount-encrypted is running on a tmpfs,
which can be detected via a W_OK check on the root filesystem.

BUG=chrome-os-partner:12033
TEST=alex build, manual test

Change-Id: I7bf5eaa244a50dd2a0de51760c964e970fa8e3aa
Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/28960
Reviewed-by: Gaurav Shah <gauravsh@chromium.org>
1 file changed