Tracker Checker (UDP): add command to monitor uptime

[josecelano]

Parent issue: #669
Relates to: torrust/torrust-demo#26

https://newtrackon.com/ is reporting a 93% uptime for the live demo UDP tracker.

When you run netstat -su you see that apparently packets are not rejected.

netstat -su
IcmpMsg:
    InType3: 49256
    InType5: 205
    InType11: 20
    OutType3: 746124
Udp:
    8187249 packets received
    1007279 packets to unknown port received
    0 packet receive errors
    8344788 packets sent
    0 receive buffer errors
    0 send buffer errors
UdpLite:
IpExt:
    OutMcastPkts: 20
    InOctets: 425726197318
    OutOctets: 862919782235
    OutMcastOctets: 800
    InNoECTPkts: 4846361527
    InECT1Pkts: 37809
    InECT0Pkts: 300510
    InCEPkts: 17275
MPTcpExt:

I have also added a new metric for the announce request proceessing time and it's low (under 10 ms):

The processing time does not include the time sending the response to the client. https://newtrackon.com/ is reporting 222 ms for the response, which is under the 10 seconds they have set for the timeout.

Therefore I don't know why the uptime is only 93%.

I want to implement a simple script which is a loop to do the same https://newtrackon.com/ does. It will make an announce request every 5 minutes printing to console:

• The total number of timeout responses
• Average response time
• Last response time
• Maximum response time
• Miminum response time

cc @da2ce7