'Given the config group name register the file.
:param config_group_name: the config group name
:returns: string -- configurationFile - name of the configuration file
:raises: VolumeBackendAPIException:'

def _register_config_file_from_config_group(self, config_group_name):

    if (config_group_name is None):
        return CINDER_EMC_CONFIG_FILE
    if hasattr(self.configuration, 'cinder_dell_emc_config_file'):
        config_file = self.configuration.cinder_dell_emc_config_file
    else:
        config_file = ('%(prefix)s%(configGroupName)s%(postfix)s' % {'prefix': CINDER_EMC_CONFIG_FILE_PREFIX, 'configGroupName': config_group_name, 'postfix': CINDER_EMC_CONFIG_FILE_POSTFIX})
    if (config_group_name not in config_file):
        config_file = ('%(prefix)s%(configGroupName)s%(postfix)s' % {'prefix': CINDER_EMC_CONFIG_FILE_PREFIX, 'configGroupName': config_group_name, 'postfix': CINDER_EMC_CONFIG_FILE_POSTFIX})
    if os.path.isfile(config_file):
        LOG.debug('Configuration    file    :    %(configurationFile)s    exists.', {'configurationFile': config_file})
    else:
        exception_message = (_('Configuration    file    %(configurationFile)s    does    not    exist.') % {'configurationFile': config_file})
        LOG.error(exception_message)
        raise exception.VolumeBackendAPIException(data=exception_message)
    return config_file
