Remove validation that causes issue #1216

[adambarreiro]

Problem

As it is now, the VCD Provider requires that default_compute_policy_id is set when vm_placement_policy_ids or vm_sizing_policy_ids are specified.

This works for most of the cases, except one important one: When a VDC is created with several Placement policies assigned (vm_placement_policy_ids) but one wants to use the System default Sizing policy as default:

resource "vcd_org_vdc" "TestAccVcdOrgVdcWithAllComputePolicies" {
  # ...omitted

  default_compute_policy_id = null # This will be computed to the System default policy, auto-generated from VCD
  vm_placement_policy_ids   = [
    vcd_vm_placement_policy.placement1.id,
    vcd_vm_placement_policy.placement2.id,
    vcd_vm_placement_policy.placement3.id,
    # ...
  ]
}

Applying a configuration like this will fail on runtime due to a validation the provider does in code:

!contains(vmComputePolicyIds, defaultPolicyId.(string))

Fix

When there is no default_compute_policy_id set (or it is ""), ignore the validation:

defaultPolicyId.(string) != "" && !contains(vmComputePolicyIds, defaultPolicyId.(string))

Tests

Added a new VDC definition that replicates this scenario in TestAccVcdOrgVdcWithAllComputePolicies

---

Closes #1216

[adambarreiro]

vm tests passed

[lvirbalas]

Few clarification suggestions inline.

[carmine73]

To avoid errors on reapply vm_sizing_policy_ids must be set to null or omitted (sorry for this comment, probably it is useful only for me).

resource "vcd_org_vdc" "TestAccVcdOrgVdcWithAllComputePolicies" {
  # ...omitted

  default_compute_policy_id = null # This will be computed to the System default policy, auto-generated from VCD
  vm_sizing_policy_ids      = null # cannot be [], otherwise leads to an error on re-apply
  vm_placement_policy_ids   = []
}