Support setting full sources list via attributes and refactor sumoconf recipe.

The major changes in this request:
1) Add support for setting the entire source list for a target host/role/environment via attributes. 
2) Refactor the sumoconf recipe to remove a lot of duplicated code and go to a single sumo.conf.erb supporting both accessid and email/pass authentication. 

The rest of the changes are minor text changes and removing an unused attribute that was in the way of the new sources definition.