Using Portal, extension seems to hang when script fails

Hi,

Forcing my script to fail, I get the following behavior:

1. In Azure, create VM.
2. Go to Extensions, Add, Select Custom Script For Linux.
3. Upload local script.
4. Click OK.

My script is:
```
#!/bin/bash
exit 1
```

**Result:**

- The Azure notification says 'The deployment to resource group xyz is in progress...'
- The notification never changes.
- The extension itself reports
```
TYPE Microsoft.OSTCExtensions.CustomScriptForLinux
VERSION 1.*
STATUS (unavailable)
STATUS LEVEL (unavailable)
STATUS MESSAGE (unavailable)
HANDLER STATUS Not Ready
HANDLER STATUS LEVEL Info
```
If I change my script to exit 0, extension installed correctly with status 'Provisioning Succeeded' (and the notification shows a success as well.

Am I doing anything wrong here?

Reproduce the issue on an Azure Linux VM with the Custom Script For Linux extension using the supplied exit 1 script, then compare it with the exit 0 case. The payload names no repository files, tests, or entry points, so begin by locating the extension provisioning and status handling; done means a failed script reports a completed, actionable failure state instead of leaving deployment permanently in progress.

Written by the indexing model from the issue text.