Compilation errors in virtualbox-cookbook recipe

 1) Typically it is not possible to use library functions in chef attribute  files. Hence using VBox::Helper   
     routine in attributes/default.rb caused compilation errors in a chef-solo run in a windows 8 box.
    (See Image below)
2) This commit moves the version detection logic from attributes/default.rb  to recipes/default.rb. And this   
     seems to work on Chef 11 via the command  'chef-solo --config solo.rb -j node.json'

![compilation error](https://cloud.githubusercontent.com/assets/6889702/2716509/192f2bce-c52c-11e3-9b73-255dc7a73e0d.png)