Guarding against `invalid memory address` in AdditionalUnattendConfig
```
make testacc TEST=./builtin/providers/azurerm TESTARGS='-run=TestAccAzureRMVirtualMachine_windowsUnattendedConfig'
==> Checking that code complies with gofmt requirements...
go generate $(go list ./... | grep -v /vendor/)
TF_ACC=1 go test ./builtin/providers/azurerm -v
-run=TestAccAzureRMVirtualMachine_windowsUnattendedConfig -timeout 120m
=== RUN TestAccAzureRMVirtualMachine_windowsUnattendedConfig
--- PASS: TestAccAzureRMVirtualMachine_windowsUnattendedConfig (943.28s)
PASS
ok github.com/hashicorp/terraform/builtin/providers/azurerm
943.299s
```
There were lots of hacky checks in the ARM VM resource to check for a
length of 1 param block
MaxItems was introduced so this PR updates to use MaxItems
When using winrm config block, we had an address issue. This is no
longer a set but a list (As a list fits it more approp)
```
make testacc TEST=./builtin/providers/azurerm
TESTARGS='-run=TestAccAzureRMVirtualMachine_'
==> Checking that code complies with gofmt requirements...
go generate $(go list ./... | grep -v /vendor/)
TF_ACC=1 go test ./builtin/providers/azurerm -v
-run=TestAccAzureRMVirtualMachine_ -timeout 120m
=== RUN TestAccAzureRMVirtualMachine_basicLinuxMachine
--- PASS: TestAccAzureRMVirtualMachine_basicLinuxMachine (587.80s)
=== RUN TestAccAzureRMVirtualMachine_tags
--- PASS: TestAccAzureRMVirtualMachine_tags (554.53s)
=== RUN TestAccAzureRMVirtualMachine_updateMachineSize
--- PASS: TestAccAzureRMVirtualMachine_updateMachineSize (612.52s)
=== RUN TestAccAzureRMVirtualMachine_basicWindowsMachine
--- PASS: TestAccAzureRMVirtualMachine_basicWindowsMachine (765.90s)
=== RUN TestAccAzureRMVirtualMachine_windowsUnattendedConfig
--- PASS: TestAccAzureRMVirtualMachine_windowsUnattendedConfig
(770.53s)
=== RUN TestAccAzureRMVirtualMachine_winRMConfig
--- PASS: TestAccAzureRMVirtualMachine_winRMConfig (827.90s)
PASS
ok github.com/hashicorp/terraform/builtin/providers/azurerm
4119.192s
```
Fixes#7053 where, when using `additional_unattend_config` in
`os_profile_windows_config` we got an error as follows:
```
azurerm_virtual_machine.test: [DEBUG] Error setting Virtual Machine
Storage OS Profile Windows Configuration: &errors.errorString{s:"Invalid
address to set: []string{\"os_profile_windows_config\", \"1534614206\",
\"additional_unattend_config\"}"}
```
The `storage_data_disk` was trying to use vhd_url rather than vhd_uri.
This was causing an error on creating a new data_disk as part of a VM
Also added validation as data_disks can only be 1 - 1023 GB in size
ssh_keys were throwing an error similar to this:
```
* azurerm_virtual_machine.test: [DEBUG] Error setting Virtual Machine
* Storage OS Profile Linux Configuration: &errors.errorString{s:"Invalid
* address to set: []string{\"os_profile_linux_config\", \"0\",
* \"ssh_keys\"}"}
```
This was because of nesting of Set within a Set in the schema. By
changing this to a List within a Set, the schema works as expected. This
means we can now set SSH Keys on VMs. This has been tested using a
remote-exec and a connection block with the ssh key
```
azurerm_virtual_machine.test: Still creating... (2m10s elapsed)
azurerm_virtual_machine.test (remote-exec): Connected!
azurerm_virtual_machine.test (remote-exec): CONNECTED!
```
adminPassword
The Azure API never returns the AdminPAssword (as is correct) from the
Read API call. Therefore on Create, we do not set the AdminPassword of
the vm as part of the state. The Same func is used for Create & Update,
therefore when we changed anything on the VM, we were getting the
following error:
```
statusCode:Conflict
serviceRequestId:f498a6c8-6e7a-420f-9788-400f18078921
statusMessage:{"error":{"code":"PropertyChangeNotAllowed","target":"adminPassword","message":"Changing property 'adminPassword' is not allowed."}}
```
To fix this, we need to excldue the AdminPassword from the Update func
if it is empty
Paul Stack