Domain id is based on hostname, which is not always unique

The domain id is now based on the hostname, which is not unique in all cases (for instance when using country_path):

public function createDomainId() {
    // We cannot reliably use sequences (1, 2, 3) because those can be different
    // across environments. Instead, we use the crc32 hash function to create a
    // unique numeric id for each domain. In some systems (Windows?) we have
    // reports of crc32 returning a negative number. Issue #2794047.
    $this->domain_id = abs((int) crc32($this->getHostname()));
  }

It should be based on id.