toolbox: add sepolicy for vendor toybox

The vendor toybox MUST always be executed without transition and
non-vendor processes are not allowed to execute the binary.

Bug: 36463595
Test: Boot and test if system shell can run /vendor/bin/echo
      Result: requires 'su'

Change-Id: Ifb9aa61f247f91fb870b99d60ac7f849ee9c6adc
Signed-off-by: Sandeep Patil <sspatil@google.com>
(cherry picked from commit c112cd18e8999c0242a2560219033231a0e19898)