security/dogtag-pki: Set the boot flag with sysrc

create_rc_service() wrote <instance>_enable="YES" into rc.conf.d, which is
read after rc.conf and therefore overrode sysrc. The instance started at boot
whatever the administrator had set, and under FreeIPA it came up before the
Directory Server it needs. The flag now goes to rc.conf through sysrc.

Sponsored by: Netzkommune GmbH