'Initialize configuration.
This takes care of grafting the implementation\'s config
values into the config group and shared defaults. We will try to
pull values from the specified \'config_group\', but fall back to
defaults from the SHARED_CONF_GROUP.'

def __init__(self, volume_opts, config_group=None):

    self.config_group = config_group
    self._ensure_config_values(volume_opts)
    self.backend_conf = CONF._get(self.config_group)
    self.shared_backend_conf = CONF._get(SHARED_CONF_GROUP)
