[GH-1977] revert and alternate fix

@mitchellh, the internal encoding doesn't seem to work.  Therefore,
I reverted that previous change to vagrant.rb.

However, I found two alternate solutions.  Either transcoding,
`/etc/redhat-release` to ISO-8859-1 on open, or using something
like File.binread to transcode the file contents to raw.
Merge pull request #2158 from atomic-penguin/GH-1977

hosts/fedora: read as encoding