"pping" command flag "-f" displays an error

xCAT man page for pping shows that `-f | --use_fping` option can be used.

When trying it, I get:

```
[root@fs4 ~]# pping -f frame23
Cannot open fping pipe: No such file or directory at /opt/xcat/bin/pping line 165.
[root@fs4 ~]# pping --use_fping frame23
Cannot open fping pipe: No such file or directory at /opt/xcat/bin/pping line 165.
[root@fs4 ~]#
```