ruby (and jruby) updates for rack/rails suites

I've cleaned up and updated the gems for the rails/rails-stripped and rack suites (both using Ruby and JRuby)

... of course we shall update more on top of it but I wanted to make sure it's less "confusing" : 
- removed unnecessary gem dependencies (from Gemfile-jruby)
- updated rack and json dependencies as well as server versions 
  + make sure they do not get auto-loaded as application libraries
- setup the latest activerecord-jdbc-adapter gem for JRuby with a "shared" database configuration
- updated rails version, (mysql) drivers

there's an issue open that would need to be revised (but is not best to get merged in it's current state anyway) https://github.com/TechEmpower/FrameworkBenchmarks/pull/847