'Creates a new TrafficMigrator.
Args:
rpcserver: The RPC server to use. Should be an instance of a subclass of
AbstractRpcServer.
app_id: The application to make the change to.
version: The version to set as the default.
error_fh: Where to send status and error messages.'

def __init__(self, rpcserver, app_id, version, error_fh=sys.stderr):

    self.rpcserver = rpcserver
    self.app_id = app_id
    self.version = version
    self.error_fh = error_fh
