package_manager.py: define info_dir and status_file when OPKGLIBDIR isn't the default

* without this the do_rootfs task doesn't respect OPKGLIBDIR and
  info, status are created in different directory than opkg on
  target expects
* people who modify OPKGLIBDIR need to make sure that opkg.conf included
  in opkg package also sets info_dir and status_file options

Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>