VMware: Set target ESX host for backing VM clone

The backing VM corresponding to a volume is cloned during create volume
from another volume, snapshot or image. The backing VM is also cloned
during retype and backup restore. Currently, the target ESX host is
unset while calling vCenter CloneVM_Task API and hence the source ESX
host is used as the target. If the destination datastore returned by
the datastore selection logic is not accessible to the source host,
clone fails. This patch fixes the problem by setting the target ESX
host (returned by datastore selection logic) while invoking clone.

Conflicts:
        cinder/volume/drivers/vmware/vmdk.py

Closes-Bug: #1380602
Change-Id: I030d5ce6378fb70f7f98356114825abc12297687
(cherry picked from commit 9e590a6c854cec6df18630954734e4a4e0249a91)
Merge "VMware: Set target ESX host for backing VM clone" into stable/juno