Add rhel8 packer template and fix centos7 and rhel7 template and kickstarts.
This changes adds a new packer template for rhel8, I have added a new kickstart template, and also fixed centos7 and rhel7 template and kickstart to 7.9 version. I changed vagrant provider from virtualbox to libvirt with kvm.
Disable consistent network interfaces names so we can use eth0 on centos7, rhel7 and rhel8. Enable gtk display for headless: false so we can debug install process.