{Bastion} az network bastion rdp fails with NullPointerException

[navba-MSFT]

fixes #6478

az network bastion rdp --name "" --resource-group "" --target-resource-id "" --disable-gateway fails with below error:

Exception in thread Thread-1 (_start_tunnel):
Traceback (most recent call last):
File "threading.py", line 1016, in _bootstrap_inner
File "threading.py", line 953, in run
File "C:\Users\francisco.nabas.azure\cliextensions\bastion\azext_bastion\custom.py", line 335, in _start_tunnel
tunnel_server.start_server()
File "C:\Users\francisco.nabas.azure\cliextensions\bastion\azext_bastion\tunnel.py", line 194, in start_server
self._listen()
File "C:\Users\francisco.nabas.azure\cliextensions\bastion\azext_bastion\tunnel.py", line 123, in _listen
auth_token = self._get_auth_token()
File "C:\Users\francisco.nabas.azure\cliextensions\bastion\azext_bastion\tunnel.py", line 110, in _get_auth_token
raise exp
msrestazure.azure_exceptions.CloudError: java.lang.NullPointerException

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[azure-client-tools-bot-prd]

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[azure-client-tools-bot-prd]

Hi @navba-MSFT,
Please write the description of changes which can be perceived by customers into HISTORY.rst.
If you want to release a new extension version, please update the version in setup.py as well.

[yonzhan]

Thank you for your contribution! We will review the pull request and get back to you soon.

[navba-MSFT]

@necusjz Could you please review this once you get a chance ?

[necusjz]

@navba-MSFT, if you wanna release a new version including this fix, please update HISTORY.rst and setup.py as well.

[azclibot]

[Release] Update index.json for extension [ bastion ] : https://dev.azure.com/azclitools/internal/_build/results?buildId=73717&view=results