title: Database cleaner wipes out all tables even when using :except option
body: <p>I'm having an issue with database cleaner on a rails project. I use a sqlite3 database in my test environment, and it has a number of tables containing reference data, populated by the db:test:prepare task, that does not need to be wiped between tests.</p>
  
  <p>I have a number of cucumber scenarios tagged with @javascript using the webdriver driver, and some without that tag.</p>
  
  <p>In my env.rb file, I have configured database cleaner to use the truncation strategy, with the except option:</p>
  
  <pre><code>DatabaseCleaner.strategy = :truncation, {:except =&gt; %w[ignore me]}
  </code></pre>
  
  <p><code>DatabaseCleaner.clean</code> is called after each scenario, and works as expected on the javascript-tagged scenarios.</p>
  
  <p>However, for the non javascript scenarios it is truncating the entire database, including the tables listed in the :except array. I've also tried calling <code>DatabaseCleaner.clean_with</code>, which didn't work either.</p>