PR 13128: Backward compatibility for stapusr and stapdev level modules.

PR 13128: Backward compatibility for stapusr and stapdev level modules.

If no privilege credentials are passed to the module, we can assume that
the module was loaded directly by a root level user (insmod) or by an
older version of staprun (less than 1.7). In the latter case, if the module
requires stapusr or stapdev credentials, we can assume that staprun did the
right thing and that the module is safe to run. Otherwise, the required
privilege level is unknown to the old staprun and we must abort.