authpolicy: Add error code for rejected passwords

To be returned by authpolicyd if an Active Directory user entered a
password on the password change screen that got rejected (e.g. too
short, same as a previous password etc.), see CL:603854.

BUG=chromium:752919
TEST=cros_run_unit_tests --board=chell --packages authpolicy

Change-Id: Id669a5b7cd0ae0a02de8b92f709b435be3bf60c1
Reviewed-on: https://chromium-review.googlesource.com/603650
Commit-Ready: Lutz Justen <ljusten@chromium.org>
Tested-by: Lutz Justen <ljusten@chromium.org>
Reviewed-by: Dan Erat <derat@chromium.org>
Reviewed-by: Roman Sorokin <rsorokin@chromium.org>
1 file changed