Use dracut-ng instead of dracut and some fixes

• freedesktop-sdk.bst: Add patches to use dracut-ng instead of dracut
• iso/initramfs.bst: drop rd.live.overlay.overlayfs
• Revert "{vm,iso}/initramfs.bst: add libkmod"
• iso/initramfs.bst: disable first boot

This completely fixes the ostree variant with systemd master. sysupdate still not tested end-to-end.