Greatly simplified Mixin::Parameters
 * All unknown methods are delegate to bag @__all directly. This enable
   to respond to any methods available to a Bag instance.
Changed a bit Bag
 * Overidde key? for indifferent access (symbol or string). Will explore
   'insensitive_hash' eventually.
Fixed Vagrant User implementation
 * We must warp mixin method_missing implementation within a
   rescue block so KeyError are properly converted to Vagrant
   exceptions.
Fix alias problem in Vagrant env command implementation
Kind of alias task tests to point to test
 * I always do the mistake :)