mydaemon: remove closeall() calls from mydaemon()

idmapd and svcgssd have a mydaemon() routine that uses closeall() to
close file descriptors. Unfortunately, they aren't using it correctly
and it ends up closing the pipe that the child process uses to talk to
its parent.

Fix this by not using closeall() in this routine and instead, just close
the file descriptors that we know need to be closed. If /dev/null can't
be opened for some reason, then just have the child exit with a non-zero
error.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve Dickson <steved@redhat.com>