provider/azurerm: Add disk_size_gb param to VM storage_os_disk (#9200)

TF_ACC=1 go test ./builtin/providers/azurerm -v -run=TestAccAzureRMVirtualMachine_basicLinuxMachine -timeout 120m
    === RUN   TestAccAzureRMVirtualMachine_basicLinuxMachine
    --- PASS: TestAccAzureRMVirtualMachine_basicLinuxMachine (540.83s)
    PASS
    ok  	github.com/hashicorp/terraform/builtin/providers/azurerm	540.841s

    TF_ACC=1 go test ./builtin/providers/azurerm -v -run=TestAccAzureRMVirtualMachine_withDataDisk -timeout 120m
    === RUN   TestAccAzureRMVirtualMachine_withDataDisk
    --- PASS: TestAccAzureRMVirtualMachine_withDataDisk (431.19s)
    PASS
    ok  	github.com/hashicorp/terraform/builtin/providers/azurerm	431.203s

builtin/providers/azurerm/resource_arm_virtual_machine.go

@@ -156,6 +156,12 @@ func resourceArmVirtualMachine() *schema.Resource {
 							Type:     schema.TypeString,
 							Required: true,
 						},
+
+						"disk_size_gb": {
+							Type:         schema.TypeInt,
+							Optional:     true,
+							ValidateFunc: validateDiskSizeGB,
+						},
 					},
 				},
 				Set: resourceArmVirtualMachineStorageOsDiskHash,
@@ -190,14 +196,7 @@ func resourceArmVirtualMachine() *schema.Resource {
 						"disk_size_gb": {
 							Type:         schema.TypeInt,
 							Required:     true,
-							ValidateFunc: func(v interface{}, k string) (ws []string, errors []error) {
+							ValidateFunc: validateDiskSizeGB,
-								value := v.(int)
-								if value < 1 || value > 1023 {
-									errors = append(errors, fmt.Errorf(
-										"The `disk_size_gb` can only be between 1 and 1023"))
-								}
-								return
-							},
 						},
 
 						"lun": {
@@ -429,6 +428,15 @@ func resourceArmVirtualMachine() *schema.Resource {
 	}
 }
 
+func validateDiskSizeGB(v interface{}, k string) (ws []string, errors []error) {
+	value := v.(int)
+	if value < 1 || value > 1023 {
+		errors = append(errors, fmt.Errorf(
+			"The `disk_size_gb` can only be between 1 and 1023"))
+	}
+	return
+}
+
 func resourceArmVirtualMachineCreate(d *schema.ResourceData, meta interface{}) error {
 	client := meta.(*ArmClient)
 	vmClient := client.vmClient
@@ -924,6 +932,9 @@ func flattenAzureRmVirtualMachineOsDisk(disk *compute.OSDisk) []interface{} {
 	result["vhd_uri"] = *disk.Vhd.URI
 	result["create_option"] = disk.CreateOption
 	result["caching"] = disk.Caching
+	if disk.DiskSizeGB != nil {
+		result["disk_size_gb"] = *disk.DiskSizeGB
+	}
 
 	return []interface{}{result}
 }
@@ -1258,5 +1269,10 @@ func expandAzureRmVirtualMachineOsDisk(d *schema.ResourceData) (*compute.OSDisk,
 		osDisk.Caching = compute.CachingTypes(v)
 	}
 
+	if v := disk["disk_size_gb"].(int); v != 0 {
+		diskSize := int32(v)
+		osDisk.DiskSizeGB = &diskSize
+	}
+
 	return osDisk, nil
 }

builtin/providers/azurerm/resource_arm_virtual_machine_test.go

@@ -524,6 +524,7 @@ resource "azurerm_virtual_machine" "test" {
         vhd_uri = "${azurerm_storage_account.test.primary_blob_endpoint}${azurerm_storage_container.test.name}/myosdisk1.vhd"
         caching = "ReadWrite"
         create_option = "FromImage"
+        disk_size_gb = "45"
     }
 
     os_profile {

website/source/docs/providers/azurerm/r/virtual_machine.html.markdown

@@ -249,6 +249,7 @@ For more information on the different example configurations, please check out t
 * `caching` - (Optional) Specifies the caching requirements.
 * `image_uri` - (Optional) Specifies the image_uri in the form publisherName:offer:skus:version. `image_uri` can also specify the [VHD uri](https://azure.microsoft.com/en-us/documentation/articles/virtual-machines-linux-cli-deploy-templates/#create-a-custom-vm-image) of a custom VM image to clone. When cloning a custom disk image the `os_type` documented below becomes required.
 * `os_type` - (Optional) Specifies the operating system Type, valid values are windows, linux.
+* `disk_size_gb` - (Optional) Specifies the size of the data disk in gigabytes.
 
 `storage_data_disk` supports the following: