Additional verification of _changes feed during long running system test

[tleyden]

After writing docs, this verification would help validate that the changes feed is returning the correct and latest revisions. (I mentioned this in today's daily standup in relation to a customer ticket).

• Get docs from _changes feed
• Get _all_docs
  • For each doc, get latest rev
  • Make sure _changes feed contains latest rev as returned from _all_docs