Add 'ip' option to the 'options' parameter for node definitions

Add the **ip** option to nodeset.yml options.

Example set definition:

```yaml
      'client.vm':
        prefab: 'centos-64-x64'
        options:
          ip: '192.168.1.5'
```

The above would add a line like this to the Vagrantfile

```ruby
    v.vm.network :private_network, :ip => '192.168.1.5'
```

It should be mentioned this does not change the primary interface's (eth0) IP address but creates a new interface (eth1).

In my tests, using Virtualbox, I did not see any issues with the second interface having conflicting MAC addresses with other nodes in the multinode tests.  Let me know if using a random MAC for this second interface would be desired.