CHEF-3404: Provider Resolver

Implements lazy evaluation of which chef provider to use based on evaluating the system.  Lets the the service resource select its provider based on interrogating the system rather than assigning a single default provider per distro.  Providers encapsulate their own logic for determining which resources they support.
Resource classes share one `node_map` instance across all resources, and Provider classes each have their own `node_map` instance.  Could we name these variables/accessors differently so that is more obvious?  Perhaps `shared_node_map` in Resource and `node_map` in Provider?