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

Make azure-mgmt-resource 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 81f2bde0a2af99d84666628fae89af648ce2fa3e)