tools: Ignore errors for frr reload stuff

tools: Ignore errors for frr reload stuff

When we pass an unknown/wrong command and do `systemctl reload frr`, all processes
are killed, and not started up.

Like doing with frr-reload.py, all good:

```
$ /usr/lib/frr/frr-reload.py --reload /etc/frr/frr.conf
vtysh failed to process new configuration: vtysh (mark file) exited with status 2:
b'line 20: % Unknown command:  neighbor 192.168.10.123 bfd 300 300\n\n'
```

Signed-off-by: Donatas Abraitis <donatas@opensourcerouting.org>
(cherry picked from commit 243e27abccf8d02caabc6ae1ea758c4bdc3069e2)