Remove use of /root/.factory_test

We are deprecating the tag file /root/.factory_test. Instead of checking
for this tag, let's check for the following two conditions to determine
if we are running factory tests:
  - 'crossystem debug_build' is 1
  - /usr/local/factory exists

BUG=chrome-os-partner:24798
TEST=Build a factory test image without .factory_test tag. Boot and
check mount-encrypted is using factory mode.
CQ-DEPEND=CL:181430

Change-Id: Ib2045cb03e3979f3d726b4ca051fd315a8039ab9
Signed-off-by: Vic (Chun-Ju) Yang <victoryang@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/181216
Reviewed-by: Richard Barnette <jrbarnette@chromium.org>
2 files changed