[Python] msrest 0.4.0 is not compatible with requests 2.11.0

[lmazuel]

The new lib requests 2.11 used as dependency of msrest is not compatible with msrest <= 0.4.0. The main reason is that requests now refuses an integer as headers value in HTTP call.

PR is on its way (I needed an issue number for the ChangeLog :))

[lmazuel]

https://pypi.python.org/pypi/msrest/0.4.1