Use Emeril to help releasing

http://fnichol.github.io/emeril/
Tweak chefignore patterns for Berkshelf to ignore vendored cookbooks
Do not delete the vendor dir after rspec run

Now that it is not copied recursively we can fasten up the dev cycle.
Default to Chef ~> 11.0 for development

Bundler seemed to use Chef v11.2.0 for some reason with the old
requirement.
Add guard-rspec setup
Move berkshelf installation to spec_helper

Copy the idea from "yum" cookbook.
Reorganize Gemfile

Remove :test group as we always want to install those gems.
Add test-kitchen gems to Gemfile

Reminder: `gem uninstall vagrant -a`
Update changelog