Constructs a Drupal\Core\FileTransfer\FileTransfer object.
$jail: The full path where all file operations performed by this object will be restricted to. This prevents the FileTransfer classes from being able to touch other parts of the filesystem.
Overrides FileTransfer::__construct
function __construct($jail, $username, $password, $hostname = 'localhost', $port = 9999) {
parent::__construct($jail, $username, $password, $hostname, $port);
}