Huawei: Implement v2 replication (managed)

Huawei: Implement v2 replication (managed)

This patch implements the managed side of v2 replication in the
HuaweiDriver. Both Synchronous mode and Asynchronous mode are
supported with Huawei arrays. The volume type need to associate with
the extra spec with 'replication_enabled' equaling to '<is> True', and
'replication_type' equaling to '<in> sync' or '<in> async'. If
'replication_type' is not provided, it will be defaulted to
Asynchronous mode.

What are supported with replication:
1. create volume
2. create volume from snapshot
3. clone a volume
4. create volume from image
5. volume retype
6. volume migration

So far we support a single remote device, and 'cinder.conf' should
configure a replication local backend and a replication remote backend
as follows:

[replica]
volume_driver =
    cinder.volume.drivers.huawei.huawei_driver.HuaweiISCSIDriver
cinder_huawei_conf_file = /etc/cinder/cinder_huawei_conf.xml
volume_backend_name = replica
replication_device = target_device_id:huawei-replica-1,
    managed_backend_name:host@replica-remote#pool,
    san_address:san_url_1;san_url_2,
    san_user:admin,san_password:passwd

[replica-remote]
volume_driver =
    cinder.volume.drivers.huawei.huawei_driver.HuaweiISCSIDriver
cinder_huawei_conf_file = /etc/cinder/cinder_huawei_conf_remote.xml
volume_backend_name = replica-remote
replication_device = target_device_id:huawei-replica-2,
    managed_backend_name:host@replica#pool,
    san_address:san_url_1;san_url_2,
    san_user:admin,san_password:passwd

Change-Id: Iaa3834547f80e7687f7e1946cb10d35f9ff0c136
Implements: blueprint support-replication-for-huawei-volume-driver