* Refs #534 Removing exit_rate from metadata API, it was added in the...

 * Refs #534 Removing exit_rate from metadata API, it was added in the standard processed metrics causing other reports to display it with 0% values
 * Refs #1465 Leave underscores in test names just to keep tests more readable (even though it is not a best practise to have _ in class prefixes!!)

git-svn-id: http://dev.piwik.org/svn/trunk@5739 59fd770c-687e-43c8-a1e3-f5a4ff64c105