Add database size comparison to verification tests

Based on the logs of several backup and verification runs the size of a restored database is typically just over 80% of the live database (~81% to 84%).

Add a test to the verification process that compares the size of the live DB with the restored DB. The test by default should look for the size of the restored DB to be not less than 80% of the live DB. This setting should be configurable on a per DB basis.