Fix config.vm.network to work

it fix  config.vm.network private_network, ip: <address>
Even when user set ip address in Vagrantfile, vagrant-kvm ignore and use predefined address in box file.
These patches fix this behavior.

- NFS machine IP address for export is recorded  when creating  network.
- Network name in libvirt network domain xml is now 'vagrant-(subnet)'
- SSH machine IP address is decided from libvirt network domain configuration.