VNX cinder driver now supports async migration during volume cloning.
By default, User can create cloned volume after the migration starts in
the VNX instead of waiting for the completion of migration. this greatly
accelerates the cloning process.
If user wants to disable this, he could add
'--metadata async_migrate=False' when creating volume from source
volume/snapshot.
DocImpact
Closes-bug: #1657966
Change-Id: Idfe5d9d4043f84cad2ae2d4d31914d3ae573de50
6ccfcafd45