Fix NFSNoHostonlyNetwork error since v0.2.2

- Regarding the commit 53065e9827

I have experienced NFSNoHostonlyNetwork error on using NFS synced folder with a boot2docker.box for Parallels which I made at https://github.com/YungSang/packer-parallels .

And then I found the deprecated "bound_to" parameter in the source code, which caused the error.

It will fix that and seems to work fine for me.
Please check it.