'Get good_function string.
Returns either the string from the driver instance or global section
in cinder.conf. If nothing is specified in cinder.conf, then try to
find the default goodness_function. When None is returned the scheduler
will give the lowest score to the driver instance.
:returns: a goodness_function string or None'

def get_goodness_function(self):

    ret_function = self.configuration.goodness_function
    if (not ret_function):
        ret_function = CONF.goodness_function
    if (not ret_function):
        ret_function = self.get_default_goodness_function()
    return ret_function
