In order to avoid spam in journald, we just get the exit code and let
the checker output the error message.
Also, correct how we retrieve process in the healthcheck_port and _listen
"ss" doesn't allow to match some processes, like "neutron-l3-agent". We
therefore use the PID instead, provided by "pgrep".
The "-d" option of pgrep allow to prepare its output for the "grep -E",
preventing any need of a loop.
(cherry picked from commit