Added new '-extra' option 'systemd_config', to check systemd service
configurations. Checks include:
* Ensure systemd services exist for each SDP init script in the
Instance Bin dir (/p4/N/bin).
* Ensure at least one systemd service exists (p4d/p4broker/p4p).
* Ensure systemd unit files match the SDP templates.
Among other things, this will detect whether the systemd service file
for p4d is using AmbientCapabilities.