provide a knob to flexibly manage the ruby requirement

Added a means to change how the r10k module deals with the ruby requirement.

We can now:

  * Maintain the default behavior via feeding the `manage_ruby_dependency`  the default value of `declare`. 
  * Feeding the `manage_ruby_dependency` parameter the value of `include` will only include the `ruby` and `ruby::dev` classes, allowing a profile for the ruby module to handle the instantiation of the ruby classes
  * Feeding the `manage_ruby_dependency` parameter the value of `ignore` will not require, include, or explicitly declare the ruby classes. It will assume that ruby is handled outside the scope of the module. 

The anchor 'r10k::ruby_done' is used to permit an ordering point for external resources to align against 



This should appease issue #66