Use UNC paths for shared folders on Windows host

plugins/providers/virtualbox/driver/version_5_0.rb

@@ -611,14 +611,9 @@ module VagrantPlugins
         def share_folders(folders)
           folders.each do |folder|
             hostpath = folder[:hostpath]
-
-=begin
-            # Removed for GH-5933 until further research.
             if Vagrant::Util::Platform.windows?
               hostpath = Vagrant::Util::Platform.windows_unc_path(hostpath)
             end
-=end
-
             args = ["--name",
               folder[:name],
               "--hostpath",