replace ckan compare source with new harvest_record table source

[rshewitt]

User Story

In order to replace ckan as a comparison source, datagov wants use the new harvest record table as the source of comparison

Acceptance Criteria

[ACs should be clearly demoable/verifiable whenever possible. Try specifying them using BDD.]

• [ ] GIVEN the harvest_record table
  AND it's populated with data
  WHEN get_ckan_records_as_id_hash is called
  THEN the necessary records will be read from the database
  AND a successful comparison will be executed.

Background

• we want to incrementally replace ckan.
• a replaceable component of ckan is the record/package table. we rely on this table to run our comparison.
• need to determine if #4669 is a prerequisite.
  • we can seed the database with test data in the meantime to move forward.

Security Considerations (required)

[Any security concerns that might be implicated in the change. "None" is OK, just be explicit here!]

Sketch

• seed the harvest record table with test data
• add a method to HarvesterDBInterface to read harvest records.
• add test verifying harvest record reading works as intended as well as comparison.