VM disk placement isn't distributed across datastores when a datastore cluster is used

/kind bug

What steps did you take and what happened: env setup:

• datastore cluster with more than one datastore
• storage policy that targets the datastore cluster
• create multiple machines using the storage policy

What did you expect to happen:

• expected the machines' disks to be distributed across all the datastores.

What actually happened:

• a single datastore is repeatedly targeted for the disk.

Environment:

• Cluster-api-provider-vsphere version:
• Kubernetes version: (use kubectl version):
• OS (e.g. from /etc/os-release):