Killing FTL via the FTL API does not fully kill FTL

[AzureMarker]

In raising this issue, I confirm the following:

• I have read and understood the contributors guide.
• The issue I am reporting can be replicated
• The issue I am reporting isn't a duplicate

How familiar are you with the codebase?:
10

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[BUG | ISSUE] Expected Behaviour:
Running echo ">kill" | nc localhost 4711 will kill FTL.

[BUG | ISSUE] Actual Behaviour:
Running the above command does not kill all of FTL.

[BUG | ISSUE] Steps to reproduce:

• Start FTL
• Run pstree pihole and see all threads running

pihole-FTL─┬─{database}
           ├─{housekeeper}
           ├─{socket listener}
           ├─{telnet-IPv4}
           └─{telnet-IPv6}

• Run echo ">kill" | nc 127.0.0.1 4711
• Run pstree pihole and see that the housekeeper and database threads have died

pihole-FTL─┬─{socket listener}
           ├─{telnet-IPv4}
           └─{telnet-IPv6}

• Run the same commands again and see that the telnet-IPv4 thread has died

pihole-FTL─┬─{socket listener}
           └─{telnet-IPv6}

• Run echo ">kill" | nc ::1 4711 to kill FTL over IPv6
• Run pstree pihole and see that the telnet-IPv6 thread has died

pihole-FTL───{socket listener}

• (Optional fun) Send the >kill command over the FTL socket to kill the socket thread. Now pstree pihole shows:

pihole-FTL

• No more ways to kill FTL over the FTL API, because there are no more FTL API listeners! Note: DNS resolution is still available.

Log file output [if available]

[2018-09-09 14:11:36.252] FTL killed by client ID: 21
[2018-09-09 14:12:15.569] FTL killed by client ID: 20
[2018-09-09 14:13:42.052] FTL killed by client ID: 18

Device specifics

Hardware Type: Tinkerboard
OS: Raspbian

This template was created based on the work of udemy-dl.

[AzureMarker]

Fixed by #395, which removes the kill command.