In order to support parallelism, ValidateAdaptor::traverseRecordStore should return results rather than modify the class state. 

This body of work should be a pure refactor, unit tests may be added to the existing interface (it will become easier to test with the returned parameter versus modifying a class member), but it should largely be supported by regression testing against existing test suites. 

The focus should primarily be on supporting Phase-1 of record store traversal. 

Returned objects should make use of merge functions added in SERVER-128593, however, until SERVER-127596 is landed, the returned objects will be the result of a full scan of the record store, and will not require merge.