CLOUDSTACK-2402. DOC. Incorporate review comments on volume snapshot enhancements for VMware.
CLOUDSTACK-4408 [Upgrade 3.0.7 to 4.2] Zone with clusters of multiple hypervisors including VMware should be processed for legacy zone.

Currently zones with multiple clusters from more than 1 hypervisor including VMware, are being ignored while processing them during upgrade.
If a zone has all non-VMware clusters then ignoring the zone is correct.
But if a zone has atleast 1 VMware cluster then make sure the zone processed further to mark it as legacy or associate the zone with appropriate VMware DC.

Signed-off-by: Sateesh Chodapuneedi <sateesh@apache.org>