VMware: place instances under resource pool

Currently, all the instances are placed under the default/root resource pool in vCenter cluster.
This does not allow to place instances in specific resource pools for specific use cases (https://tinyurl.com/wspnmu28)

This blueprint will group instances under specific cluster and resource pool on vCenter whose name
matches the cluster_name and resource_pool_name. If no resource_pool_name is defined, instances would be grouped under the default/root resource pool. Thus, the change is backward compatible and affects only new instances.

Also, there would be no change in user or tenant workflow.