Cable connected

There are two commits in this pull request:

My first commit directly addresses my cableconnected issue. I have verified this on my local machine using the versions listed in the issue.
Commit   cd0c7dfbd9633bc10760436be63292d50a95ad38
Please see:   https://github.com/mitchellh/vagrant/issues/2890

The second commit is where I backported this same code to the earlier 4.x virtualbox drivers
I have not tested them specifically against those virtualbox releases.
I committed that code separately, so you have flexibility in regards to testing/discarding/merging.