mkcloud-libvirt: remove and add iptables rules
mkcloud-libvirt: remove and add iptables rules

Libvirt removes and adds (at top) its iptables reject rules
upon net-delete/create
so we need to do the same, so that our accept rules
come before libvirt's reject rules.

Without this change, you get a working 1st run with
1. our accept
2. libvirts reject

and a broken 2nd run with
1. libvirts reject
2. our accept

This is a partial revert of commit 10572913

gosipyan/automation,aspiers/automation,SUSE-Cloud/automation,gosipyan/automation,vmoravec/automation,SUSE-Cloud/automation,gosipyan/automation,aspiers/automation,vmoravec/automation,aspiers/automation,gosipyan/automation,aspiers/automation,SUSE-Cloud/automation,SUSE-Cloud/automation,vmoravec/automation,vmoravec/automation