Router pinging is using an unstable interface

[horcsinbalint]

https://github.com/EotvosCollegium/mars/blob/c90d73a75bb5f9429b7cfd0d6b073152631861d3/app/Console/Commands.php#L75C1-L75C106 uses the ping command's output to determine whether a router is available. If a router is available, then it works fine but if a router is not available, sometimes it might misinterpret the results as the ping command might give out failed results without those words present as per https://github.com/iputils/iputils/blob/294a65f00047f31685b7dd07048b48c4be82e097/ping/ping.c#L1236
It is not just some theoretical issue, as it has sent a couple of emails because of one router.

[horcsinbalint]

We should probably use nmap for it as it has multiple output formats that can be easily processed. Probably all routers can be pinged with a single command. For example nmap IPADDRESSHERE -sP -oG - can be easily processed (like it contains the IP address and the Status: Up string if the pinging is successful and it can process multiple IP-s in a single command).