Changed ruby::dev package defaults to something more useful for RHEL 5 and 6.

There's no package "rubygems-bundler" available on RHEL5 or RHEL6, and installing bundler doesn't seem strictly necessary anyway, so I removed it and replaced it with some more useful ruby-devel packages. If someone who uses RedHat deems it necessary in the future to install bundler using ruby::dev, they can put in some code to set "provider => gem" for bundler and install it using gem.