Port forward with iptables for VMs on libvirt based NAT network

Quite often I felt the need to setup port forwarding from the libvirt hypervisors public IP to the IP of the VM instance which is connected to a private network behind a NAT.
This way I can provide access these VMs from outside the Hypervisor.

This simple script gain Iptables based port forwarding for libvirt hosted kvm/lxc instances.
It takes input of the form <host_port>:<dest_ip>:<dest_port> or in this case <hypervisor_port>:<vm_ip>:<vm_port>