Cleanup Systemd unit file

[amiryal]

Prompted by @solarkennedy’s reply, here is how I think the Systemd unit file should look.

One thing that is not addressed in the very detailed commit message is the request for “some good data on what [the value of RestartSec] should be”. My reasoning for removing this option and keeping the default is as follows:

1. My intuition tells me that we want to respawn Consul immediately on failure, without any delay. This would have meant setting RestartSec=0ms.

2. The creators of Systemd, and Systemd itself by extension, are notorious for being very opinionated. If they deemed that the default should be 100ms and not 0ms, and given that I don’t have data to support my preference, I will rather trust their judgement.

The full commit message follows:

Remove references to basic.target: Systemd automatically adds
dependencies of the types Requires= and After= for this target unit to
all services, so KISS and DRY.

Remove KillMode= option: Consul itself runs entirely in one process, so
the default of killing all processes in the control group would not make
a difference. If Consul does spawn processes, e.g. for health checks,
the previous setting would have left them running behind when the
service is stopped.

Remove RestartSec= option: There is no reason to override the default of
100ms.