Refactor chef_object_db add_to_solr to use new chef_object behavior

This motivates the need for chef_object:is_indexed as a callback and
simplifies adding and deleting objects to solr via the indexing queue
such that there is a clear pattern of the object getting to define
whether it belongs in the index or not.
Refactor delete and delete_from_db in chef_object_db

Here's how we'd like this level of the code to work with chef_db for
object delete.
Squash with new add_to_solr