systemctl: don't suppress error code when handling legacy commands

systemctl: don't suppress error code when handling legacy commands

For legacy commands such as /sbin/halt or /sbin/poweroff we support legacy
fallbacks that talk via traditional SysV way with PID 1 to issue the desired
operation. We do this on any kind of error if the primary method of operation
fails. When this is the case we suppress any error message that is normally
generated, in order to not confuse the user. When suppressing this log message,
don't suppress the original error code, because there's really no reason to.