koops: parse taint flags

- flag taint_virtual_box was removed because it does not exist (or does
  it?), taint_module_gpl removed due to it being the negation of
  taint_module_proprietary
- the json format is a bit more compact than was originally intended

Signed-off-by: Martin Milata <mmilata@redhat.com>
Signed-off-by: Michal Toman <mtoman@redhat.com>