Fixed Gemfile formatting and Vagrant v2 revision
 * We now install 1.3.5.
Improved error reporting when a parameter cannot be found
 * Fixes #8
 * A error inheriting from VagrantError is raised with a nice
   (an translatable) error message.
Improved testing Vagrantfiles
 * Some of them were missing a parameter definition and added
   mirror for v1.
Merge branch 'feature-friendly-error-message' into 1.x