Merge pull request #5939 from jsquyres/pr/coverity-cid-1440332

opal/os_path: fix minor string overrun

opal/util/os_path.c

@@ -59,7 +59,7 @@ char *opal_os_path(int relative, ...)
     	if (relative) {
             path[0] = '.';
         }
-        strncat(path, path_sep, len);
+        strncat(path, path_sep, len - 1);
     	return(path);
     }