On Platform.sh or other setups where ideally disk should not be writable, attempting to set this up will be blocked by installer as it no matter what is configured as cache service attempts to clear cache on disk.

Second issue here is that installer actually don't clear cache when setup is configured for redis/memcached. This can be an issue when performing install on existing setup with existing data already in cache.

Besides that the cache clearing logic in installer is today breaking with Symfony 3.4, so needs to be fixed anyway.