Since requests 2.5.3, there is an issue on import affecting the setup.py Python 2.6 and 2.7 builds. I've already reported an issue upstream. But wanted to open a bug report here for house keeping and in case it's not an upstream issue. Build 2018 did finished some jobs which now fail since build 2019.
There might be also a connection to T85717 which also causes errors on the Python 3.4 jobs (again only the setup.py ones).