add better error message for missing datastore

[mikemorency]

SUMMARY

If you try to add a datastore that does not exist to the allowed datastores list in the vCLS config, you get a cryptic error message. If a user encounters the error, its really not clear what went wrong.

This change adds a more descriptive error message in the case that the datastore a user tries to add cannot be found.
I deconstructed the existing method a bit as well, since it was beginning to get large and complex.

ISSUE TYPE

• Feature Pull Request

COMPONENT NAME

vmware_cluster_vcls

ADDITIONAL INFORMATION

Test Playbook:

- hosts: localhost
  gather_facts: false
  tasks:
  - name: Configure vCLS Datastore Settings
    community.vmware.vmware_cluster_vcls:
      hostname: foo
      username: foo
      password: foo
      datacenter_name: foo
      cluster_name: foo
      allowed_datastores: ["doesnotexist"]

Before:

TASK [Configure vCLS Datastore Settings] ********************************************************************************
fatal: [mikemorency]: FAILED! => {"changed": false, "msg": "('A specified parameter was not correct: spec.systemVMsConfig.allowedDatastores[1].key', None)"}

After:

TASK [Configure vCLS Datastore Settings] ********************************************************************************
fatal: [mikemorency]: FAILED! => {"changed": false, "msg": "Failed to add datastore 'doesnotexist' because it does not exist."}

[mikemorency]

@mariolenz hoping i didnt miss the june release cutoff 🤞

[softwarefactory-project-zuul]

Build succeeded.
https://ansible.softwarefactory-project.io/zuul/buildset/7b8a8abf1d4749c6a104869fbf8e3d51

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