azure backend not working with german servers

[Max Halldén]

I checked out the latest version with bzr branch lp:duplicity yesterday and it worked fine with a regular account, but when I switched to Azure Germany things stopped working. The german servers are separate from the others because of german privacy laws.

I have attached a patch adding the variable AZURE_ENDPOINT_SUFFIX to the azure backend. When I set this to "core.cloudapi.de" it works for me with the Azure Germany account. Other (non-german) account still working with patch when variable isn't set.