Fix unit tests.  Modified sleep for DB key/cert to break out and fail if sleep is set to 0.
Enhanced unit tests to increase coverage.
Bug where db_limit_max_entry_size wasn't initialized.  Now set to current DB limit.  In reality it'll be set when CT starts up, but for unit tests, need to set it to something relatively large.
Modified clear_removed_peers to pass in peers whose index has really been removed.  This is to counter the problem where the db_tool has gotten the peers and removed the indexes of the removed_peers.  But it takes long enough that new peers are placed in the removed_peers set, but have not yet had their indexes removed.