WebTestCase::loadFixtureFiles with append=false using ODM fails

Nobody has claimed this yet.

When attempting to use `\Liip\FunctionalTestBundle\Test\WebTestCase::loadFixtureFiles()` passing in `append=false`, I encountered an error. I believe it has to do with detection of the DB platform as shown in [L382-L394](https://github.com/liip/LiipFunctionalTestBundle/blob/master/Test/WebTestCase.php#L382-L394).

My workaround, presently, is as follows:

``` php
/**
* @inheritDoc
*/
public function loadFixtureFiles(array $paths = [], $append = false, $omName = null, $registryName = 'doctrine')
{
$om = $this->getObjectManager($omName, $registryName);

if ($append == false && ($om instanceof DocumentManager)) {
$sm = $om->getSchemaManager();

$sm->dropDatabases();
$sm->createDatabases();
}

parent::loadFixtureFiles($paths, true, $omName, $registryName);
}
```

Not sure if that would be the ideal approach, or if there's a better platform agnostic way of determining which class methods need to be called for a reset. Just wanted to call it out for a future release!

Start at Test/WebTestCase.php lines 382-394 and trace loadFixtureFiles() when append=false with an ODM DocumentManager. Compare the reported workaround with the existing database-platform detection and determine the platform-agnostic reset path. Done means the method no longer fails for ODM usage with append=false; no test file is named in the issue.

Written by the indexing model from the issue text.