fix: r/vsphere_nas_datastore not mounted to additional hosts as day-two

[stoyan-hristov]

Fix a bug in nasDatastoreMountProcessor.diff() method which was the root cause of #1589

Description

Fix r/vsphere_nas_datastore not mounted to additional hosts as day-two.

The nasDatastoreMountProcessor.diff() method was not correctly calculating the difference between the old and the new datastore hosts and as a result of this the nasDatastoreMountProcessor.processMountOperations()was not mounting the datastore the new hosts.

Testing done:
Added additional ESXi hosts to the "host_system_ids" of NFS datastore and verified that terraform apply correctly mounted the datastore to the new hosts.

Closes #1589

Acceptance tests

• Have you added an acceptance test for the functionality being added?
• Have you run the acceptance tests on this branch?

Output from acceptance testing:

% make testacc TESTARGS="-run='TestAccResourceVSphereNasDatastore'"
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go test $(go list ./... |grep -v 'vendor') -v -run='TestAccResourceVSphereNasDatastore' -timeout 240m
?   	github.com/hashicorp/terraform-provider-vsphere	[no test files]
=== RUN   TestAccResourceVSphereNasDatastore_basic
--- PASS: TestAccResourceVSphereNasDatastore_basic (95.16s)
=== RUN   TestAccResourceVSphereNasDatastore_multiHost
--- PASS: TestAccResourceVSphereNasDatastore_multiHost (85.58s)
=== RUN   TestAccResourceVSphereNasDatastore_basicToMultiHost
--- PASS: TestAccResourceVSphereNasDatastore_basicToMultiHost (115.49s)
=== RUN   TestAccResourceVSphereNasDatastore_multiHostToBasic
--- PASS: TestAccResourceVSphereNasDatastore_multiHostToBasic (114.27s)
=== RUN   TestAccResourceVSphereNasDatastore_renameDatastore
--- PASS: TestAccResourceVSphereNasDatastore_renameDatastore (121.41s)
=== RUN   TestAccResourceVSphereNasDatastore_inFolder
--- PASS: TestAccResourceVSphereNasDatastore_inFolder (94.32s)
=== RUN   TestAccResourceVSphereNasDatastore_moveToFolder
--- PASS: TestAccResourceVSphereNasDatastore_moveToFolder (126.15s)
=== RUN   TestAccResourceVSphereNasDatastore_inDatastoreCluster
--- PASS: TestAccResourceVSphereNasDatastore_inDatastoreCluster (97.25s)
=== RUN   TestAccResourceVSphereNasDatastore_moveToDatastoreCluster
--- PASS: TestAccResourceVSphereNasDatastore_moveToDatastoreCluster (125.42s)
=== RUN   TestAccResourceVSphereNasDatastore_singleTag
--- PASS: TestAccResourceVSphereNasDatastore_singleTag (93.48s)
=== RUN   TestAccResourceVSphereNasDatastore_modifyTags
--- PASS: TestAccResourceVSphereNasDatastore_modifyTags (128.06s)
=== RUN   TestAccResourceVSphereNasDatastore_singleCustomAttribute
--- PASS: TestAccResourceVSphereNasDatastore_singleCustomAttribute (87.62s)
=== RUN   TestAccResourceVSphereNasDatastore_multiCustomAttribute
--- PASS: TestAccResourceVSphereNasDatastore_multiCustomAttribute (119.52s)
PASS
``

### Release Note
Release note for [CHANGELOG](https://github.com/hashicorp/terraform-provider-vsphere/blob/main/CHANGELOG.md):
Bug fix:

`r/vsphere_nas_datastore` not mounted to additional hosts as day-two https://github.com/hashicorp/terraform-provider-vsphere/issues/1589

### References

https://github.com/hashicorp/terraform-provider-vsphere/issues/1589

[hashicorp-cla]

All committers have signed the CLA.

[tenthirtyam]

Thank you, @stoyan-hristov.

Sucessfully tested and approved. 🚀

[github-actions]

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