Introduce user defined configuration cookbooks for customizing sumo.json and/or sumo.conf

In this PR I have added two user definable custom configuration cookbook 
and template attributes for sumo.json and sumo.conf.  These attributes 
allow someone using the community sumologic-collector cookbook to inject 
their own custom sumo.json and sumo.conf templates through custom 
cookbooks directly or from a wrapper cookbook.  Included default attributes 
ensures that all current sumologic-collector cookbook behavior remains the 
same unless a user wants to introduce custom configuration cookbooks and 
templates.

I realize this PR adds a bit of complexity to the cookbook but I've maintained 
the current functionality and provided more flexibility for configuring sumo.json
and sumo.conf.  I think this is a good alternative until the cookbook contains 
proper LWRP's for configuring log sources.