Fix NFSNoHostonlyNetwork error since v0.2.2

- Regarding the commit 53065e9827
https://github.com/Parallels/vagrant-parallels/commit/53065e98271d5d09fcf2f28ea3402543eaa20ff5
Merge pull request #95 from YungSang/nfs

Fix NFSNoHostonlyNetwork error since v0.2.2