Initial import of 'centos-ruby' image based on SCL and puma

This image provide Ruby 1.9.3 using SCL and `puma` web server that runs the Ruby application.

It has several improvements from the original 'rbenv' based image:

* It does not compile Ruby but use the SCL system Ruby
* It runs faster puma web server
* It provides development files and libraries to allow build gems like 'mysql2' or 'pg' or 'nokogiri'...
* Bundler install just dependencies necessary for 'production' deployment