[bugfix] [RHEL/6] Fix OOM killer termination of oscap probe_file process due to excessive memory use when evaluating file_permissions_ungroupowned rule

Today I got hit by the following issue:
  [1] https://www.redhat.com/archives/open-scap-list/2014-May/msg00005.html

When oscap process (probe_file child of it) was trying to evaluate file_permissions_ungroupowned RHEL-6 rule it got killed by OOM killer & ended up with the following error message:

```
# oscap oval eval --id oval:ssg:def:334 ssg-rhel6-oval.xml
Definition oval:ssg:def:334: not evaluated
OpenSCAP Error: Unable to close probe sd [oval_probe_ext.c:565]
No definition with ID: oval:ssg:def:334 in result model. [oval_agent.c:184]
```

The very same issue has been corrected for ```no_files_unowned_by_user``` OVAL check via patch:
  [2] https://github.com/OpenSCAP/scap-security-guide/commit/2eeeca75499f69adeb74f63e9f667c2460ae2435

But looks case [1] / case of ```file_permissions_ungroupowned``` RHEL-6 OVAL rule wasn't fixed yet.
Thus correct it.

Please review.

Thanks, Jan.