First functional kitchen.ci commit

This commit doesn't ship any tests. It adds Gemfile with gem
depedencies, adds missing dependency into formula requirements
and adds kitchen related bits into gitignore file.
Added basic serverspec tests for Redis.
Cosmetic change - removed omnibus_ruby_requirement.
Enabled vagrant-cachier if it's installed
Omnibus chef download is now cached
Removed Vagrant.erb
Updated Gemfile.lock
Making kitchen tests available in Jenkins
Add missing deps to get tests running under kitchen
Tests on AWS ready to run
Merge pull request #5 from ministryofjustice/kitchen-salt

Initial Kitchen salt