dhcpd6: move '-cf /etc/dhcp/dhcpd6.conf' from sysconfig/dhcpd6 to dhcpd6.service
run 'chown -R dhcpd:dhcpd /var/lib/dhcpd/' before starting dhcpd/dhcpd6 service
for the case where leases file is owned by root:root as a
consequence of running dhcpd without '-user dhcpd -group dhcpd' (#744292)
Use '--enable-paranoia --enable-early-chroot' configure flags
Create/delete dhcpd user in %post/%postun
Run dhcpd/dhcpd6 services with '-user dhcpd -group dhcpd'
