[Cache] give control over cache prefix seed

The configurable cache prefix seed does not give full control over the cache prefix because the container class is added to the prefix in any case. This is a problem because the container class contains the app env name. We use different app environments for different deployment targets (dev and test). Dev and test should use the same redis cache. But this is impossible to achieve because even setting the cache prefix seed does not accomplish this.

Author: Tobion

Tests/DependencyInjection/SecurityExtensionTest.php

@@ -365,6 +365,7 @@ public function testRememberMeCookieInheritFrameworkSessionCookie($config, $same
         $container->setParameter('kernel.bundles_metadata', []);
         $container->setParameter('kernel.project_dir', __DIR__);
         $container->setParameter('kernel.cache_dir', __DIR__);
+        $container->setParameter('kernel.container_class', 'app');
 
         $container->loadFromExtension('security', [
             'firewalls' => [