Move the server PID file to /var/run for the System V Linuxes

We should move the PID file to /var/run - in a fashion similar to how we do it for moxi. /var/run is considered "tmpfs" and is cleared on reboot. VM / host abrupt restart is a failure mode that folks see from time to time and we'd like to clear the PID file in these cases.

We only need to do this for the System V Linuxes - RedHat / CentOS 6; Ubuntu / Debian 12, 14; SUSE 11 as we integrate as a "simple service" with systemd where it's available and as we eschew PID files altogether.

There's a separate ticket against ns_server to track removal of the PID file in graceful shutdown cases (MB-24291) - which is appropriate because ns_server creates the PID file.