add test cookbook for rvm installation

* test-kitchen needs its own bundle group
* project-specific Cheffile addition for rvm
* create a test cookbook to do the rvm installation/setup for running
  tests
* remove "rvm baseboxes" for supported platforms, use test-kitchen
  defaults

Output of 'bundle exec kitchen test --platform ubuntu-12.04:

Finished in 15.2 seconds
99 examples, 0 failures

1 files changed, 4 insertions, 0 deletions

diff --git a/Gemfile b/Gemfile
index 9d42572..6450af9 100644
--- a/Gemfile
+++ b/Gemfile
@@ -8,4 +8,8 @@ group(:test) do
 
 end
 
+group(:kitchen) do
 
+  gem 'test-kitchen', '>= 0.7.0.beta.1'
+
+end