The systemd configs spread across our repo were fairly out of sync. This
should get them on our best practices.
The deployment guide also had some strange things like running Nomad as
a non-root user. It would be fine for servers but completely breaks
clients. For simplicity I simply removed the non-root user references.
systemd limits the number of process and threads you can create within the cgroup it creates for a given service. This is especially limiting if you have a high number of keys Nomad watches from Consul.
Fixes#4649
The default (control-group) kill mode in systemd will kill the associated executors, leading to a commonly seen behavior of nomad client restarts losing all current allocations.
setting the KillSignal to SIGINT seems to be a reasonable default, and allows things like leave_on_interrupt to function
The existing nomad.service is having minor configuration and this change
adds the following:
* Install section that allows nomad to be able enabled in systemd
* Default limit of open files is set to 65536
