Fixes for volume creation

[okrause]

• Fix for issue Error creating/modifying volumecode: 400, message: Modification of Root Access is not available for SO volumes #90
• Fix for issue code: 400, message: Error updating volume - Cannot specify NFSv3 export policy rules for non-NFSv3 volume #92

I took a stab at fixing the two recent issues. I successfully tested volume creation, re-applies, changes and deletes of NFSv4 CVS-Performance volumes and NFSv3 CVS-Software volumes.

[okrause]

@wenjun666 Please have a look.

[okrause]

The fix has merge conflicts, since it reverts most changes from latest commit f3a8f75

[okrause]

Here my environment specific code I used to test the changes.

# local variables
locals {
  network = "cvs-prd-shared-vpc"
  volume_name = "terraform-nfs-example"
  region = "us-west4"
  size = 1024
  service_level = "premium"
}

resource "netapp-gcp_volume" "gcp-volume-nfs" {
  name = local.volume_name
  region = local.region
  protocol_types = ["NFSv4"]
  network = local.network
  # When working with shared VPC, specify project number of host project
  # shared_vpc_project_number = "<hosting_project_number>"
  size = local.size
  service_level = local.service_level
  # storage_class: choose "software for CVS, choose "hardware" for CVS-Performance
  storage_class = "hardware"
  # zone: For storage_class = "software" specification of zone is required
  # zone = "europe-west1-b"
 
  # up to 5 export rules
  export_policy {
    rule {
      allowed_clients = "10.0.1.0/24"
      access          = "ReadWrite"
      has_root_access = true
      nfsv3 {
        checked = false
      }
      nfsv4 {
        checked = true
      }
    }
  }
}

resource "netapp-gcp_volume" "nfs_cvs" {
  name                     = "cvs-volume"
  pool_id                  = "6f37bb03-9da9-5682-661f-717a670ca507"
  size                     = 128
  volume_path              = "test"
  region                   = "us-east1"
  zone                     = "us-east1-b"
  network                  = local.network
  regional_ha              = true
  storage_class            = "software"
  service_level            = "standard"
  delete_on_creation_error = true
  protocol_types           = ["NFSv3"]
  export_policy {
    rule {
      access          = "ReadWrite"
      allowed_clients = "10.0.0.0/8"
      has_root_access = true
      nfsv3 {
        checked = true
      }
      nfsv4 {
        checked = false
      }
    }
  }
  unix_permissions = "0755"
}

One caveat: To make it work and generate stable plans, CVS-SO volumes need the full

      nfsv3 {
        checked = true
      }
      nfsv4 {
        checked = false
      }

in the HCL code. You cannot omit the nfsv4 part.

Also, I found out that changes e.g. to size still trigger the "Modification of Root Access is not available for SO volumes" error. The PR is incomplete.

[okrause]

The new commit is supposed to make changes/updates of CVS-Software volumes work.