Configuring multi-storage support

Example for configuring multiple storage systems:

enabled_backends = t_fc, 18000_fc
[t_fc]
volume_driver = cinder.volume.drivers.huawei.huawei_t.HuaweiTFCDriver
cinder_huawei_conf_file = /etc/cinder/cinder_huawei_conf_t_fc.xml
volume_backend_name = HuaweiTFCDriver
[18000_fc]
volume_driver = cinder.volume.drivers.huawei.huawei_driver.Huawei18000FCDriver
cinder_huawei_conf_file = /etc/cinder/cinder_huawei_conf_18000_fc.xml
volume_backend_name = Huawei18000FCDriver