install.sh could fail in az login failure, blocking following installation steps

```
No VM guests are running outdated hypervisor (qemu) binaries on this host.
SUCCESS: Azure CLI installed successfully
INFO: Checking Azure CLI authentication...
INFO: Checking Azure CLI authentication for user: root
WARNING: Azure CLI is not authenticated for user: root
INFO:
INFO: If you want to use Azure CLI authentication:
INFO: 1. Exit this installer (Ctrl+C)
INFO: 2. Run 'az login' as user root
INFO: 3. Then re-run this installer with sudo
INFO:
Do you want to continue anyway? Azure Arc will not work with CLI authentication [y/N]
```

Start with install.sh and reproduce the Azure CLI authentication path around az login; trace how a failed or declined authentication result is handled. Done means the installer no longer blocks or exits before later installation steps when authentication fails, while preserving the Azure Arc warning.

Written by the indexing model from the issue text.