Use SWIG_fail in %exception upon throwing OSError for errno

Unfortunately SWIG_exception does not support throwing OSError, so this
still requires Python-specific code.

Unlike just returning NULL, this will clean up intermediate allocations.

Signed-off-by: Ryan Lee <ryan.lee@canonical.com>

libraries/libapparmor/swig/SWIG/libapparmor.i

@@ -31,8 +31,9 @@ extern int _aa_is_blacklisted(const char *name);
 %exception {
   $action
   if (result < 0) {
+    // Unfortunately SWIG_exception does not support OSError
     PyErr_SetFromErrno(PyExc_OSError);
-    return NULL;
+    SWIG_fail;
   }
 }
 #endif