Do not extend scope, but replace it

[lmazuel]

 self.credential_scopes = ['https://management.azure.com/.default'] 
 self.credential_scopes.extend(kwargs.pop('credential_scopes', [])) 

should be:

self.credential_scopes = kwargs.pop('credential_scopes', ['https://management.azure.com/.default'])

See Azure/azure-sdk-for-python#12947 for details