Avoid false positives when Installation folder removal

[javigomez]

Even after #43 we are still having false positives:

`Error: execute joomla installation (1stInstallJoomlaTestCept)``

We need to test using $I->waitForElementChange() instead. See: https://github.com/Codeception/Codeception/blob/2.1/src/Codeception/Module/WebDriver.php#L1497-L1522

[javigomez]

reopening

See #51