Make azure-mgmt-... work with requests 2.11.x. We should update the azure...

Make azure-mgmt-... work with requests 2.11.x. We should update the azure python packages, however, that is a much bigger effort. This is needed to make sure nixops keeps working with Azure.

(cherry picked from commit 4eb92c5c64906a5142e7cb34bdcfc7e16ab77dd1)