lab vm create fails with NotSpecified/NativeCommandError

### Description
Copy attached Artifacts.json into working folder (c:\temp).
Start Windows Powershell ISE as Administrator.
Change directory to working folder.
Authenticate with Azure using: ```az login```
Execute the following command:
```
az lab vm create --lab-name "dtlLocust" --resource-group "rglocust" --name "Master" --formula "dc16Locust" --artifacts "./artifacts.json"
```

Returns the following error:
```
az : ERROR: Expecting value: line 1 column 1 (char 0)
At line:1 char:1
+ az lab vm create --lab-name "dtlLocust" --resource-group "rglocust" - ...
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo : NotSpecified: (ERROR: Expectin...lumn 1 (char 0):String) [], RemoteException
+ FullyQualifiedErrorId : NativeCommandError
```

Resources specified within command have been successfully verified to exist using other CLI 2.0 commands (e.g. group exists, lab get, lab formula list).
The artifacts.json file (attached) was created using the ```az lab formula export-artifacts``` command and piping through powershells ```Out-File```.

No additional debug information output after changing $DebugPreference="Continue" as recommended on PS GitHub. Have also tried --debug and --verbose switches with no effect.

Using the powershell command: ```$Error[1] | ConvertTo-Json``` gives the additional information in the attached error.json.
[az-lab-vm-create-error-files.zip](https://github.com/Azure/azure-cli/files/1281567/az-lab-vm-create-error-files.zip)

---

### Environment summary

**Install Method:** How did you install the CLI? (e.g. pip, interactive script, apt-get, Docker, MSI, nightly)
MSI

**CLI Version:** What version of the CLI and modules are installed? (Use `az --version`)
azure-cli (2.0.16) / lab (0.0.10)

**OS Version:** What OS and version are you using?
Windows 6.1.7601.65536

**Shell Type:** What shell are you using? (e.g. bash, cmd.exe, Bash on Windows)
Powershell 5.0.10586.117