daemon: set FD_CLOEXEC on per-port out= and err= paths

daemon: set FD_CLOEXEC on per-port out= and err= paths

Neither xap_helper nor git(1) subprocesses we spawn use the the
per-port log files we can assign to the daemon processes.  So
ensure these per-port standard err= and out= log files do not
stay open and run servers out-of-space.

Furthermore, we can rely on autodie::fnctl throughout Daemon.pm
to detect errors and remove explicit error checking.