Fix to avoid poor $PATH values

For now, there's much servers where SMART values is absent. It's because `cron` PATH contains only:
```
# cron
/usr/bin:/bin
# generic
/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
```

Here's the hotfix - not tested much, but worked fine for about 3 servers.

Also, the `which smartctl` could be better, regarding to it's flexibility.

And the other way is to fix $PATH right inside the `/etc/cron.d/storage-system-monitoring-fastvps`