Native support for systemd in ProcMon

Currently, ProcMon has no native support for systemd. As a result, whenever "systemctl start columsntore" is issued, the prompt is returned immediately (because an intermediate shell script run.sh is used). This creates the false sense that the service has been fully started - which is not true, as it may take up to a minute to do so (e.g., after a backup has been restored).

Implementing systemd support is not hard. ProcMon should be linked to libsystemd and it should wait until all expected ColumnStore processes are all truly started/synchronised/whatever, then call

sd_notify(0, "READY=1");

The current startup script run.sh should no longer be used with systemd, but could be retained for cases when systemd is not available (if such exists at all).

With native sytsmed support the unit file for ColumnStore should specific longer startup timeout than the default; also, longer wait time before scheduled restart in case of failure may be useful too.