daemons: write pid file even when told not to daemonize

systemd wants to run daemons in foreground, but daemons wouldn't write
out the pid file with -f.  Fixed.

Signed-off-by: Alexandre Oliva <oliva@gnu.org>
Merge pull request #2468 from dachary/wip-always-create-pidfile

daemons: write pid file even when told not to daemonize

Reviewed-by: Loic Dachary <loic-201408@dachary.org>
Reviewed-by: Sage Weil <sage@redhat.com>