'Take a host_id and a new_vuln amount and modify the string representation
and the vuln amount of the host of id host_id in the model according
to the new_vuln_amount. Return None.
@preconditions: host_id must be in self.host_id_to_iter,
self.host_id_to_iter[host_id] must in the model.'

def _modify_vuln_amount_of_single_host_in_model(self, host_id, new_vuln_amount):

    if (not self._is_host_in_model_by_host_id(host_id)):
        return
    host_iter = self.host_id_to_iter[host_id]
    current_host_name = self.model[host_iter][3].split('    ')[0]
    new_host_string = '{0}    ({1})'.format(current_host_name, new_vuln_amount)
    self.model.set_value(host_iter, 4, new_vuln_amount)
    self.model.set_value(host_iter, 3, new_host_string)
