Move cache and log dir to shared memory

appkernel.php

public function getCacheDir()
    {
        if (in_array($this->environment, array('dev'))) {
            return '/dev/shm/site/cache/' . $this->environment;
        }

        return parent::getCacheDir();
    }

    public function getLogDir()
    {
        if (in_array($this->environment, array('dev'))) {
            return '/dev/shm/site/logs';
        }

        return parent::getLogDir();
    }