VNX: Replication V2 support(managed)

VNX: Replication V2 support(managed)

This patch implements the managed side of replication V2 in VNX driver.

cinder.conf should follow below examples:

[vnx_cinder]
...
replication_device = target_device_id:<vnx serial number>,
                     managed_backend_name:
                     <host>@<backend_name>#<pool_name>,
                     san_ip:192.168.1.2,
                     san_login:admin,
                     san_password:admin,
                     storage_vnx_authentication_type:global,
                     storage_vnx_security_file_dir:/home/stack
...

Supported operation:
* create volume
* disable replication
* enable replication
* failover replication
* clone volume
* create volume from snapshot

VNX cinder driver also supports failover back and forth

NOTE: you can only place one replication_device for each backend since
VNX driver only supports 1:1 fanout ratio. Only synchronized replication
is supported in this patch.

DocImpact
Change-Id: Ica47700b0f251bb4f7af5500f36416ddf91de9c5
Implements: blueprint vnx-replication-v2