…for windows

Prior to this commit, vagrant was not grabbing all of the tokens on
Windows for showing the full drive because the ruby api for it behaves
differenly on windows compared to other platforms. This commit changes
that by ensuring the letter drive is attached to the path when showing
an exception.

…ions

Prior to this commit, if there was a config error inside a provider
block, Vagrant wouldn't grab the right backtrace token on windows since
the api is different for ruby on Windows compared to all other
platforms. This commit ensures that the proper line number is chosen so
the error message is correct.