fixes #7705 - adding errata counts to content host details

This brings errata, repository association to errata, and applicable errata for systems into
the database. Also remove the Errata class that was based on Elasticsearch
Merge pull request #4705 from jlsherrill/db_errata

fixes #7705 - adding errata counts to content host details
Refs #6421: Fix spec directory rubocop offenses.