LFMF: If your python build is failing, it's setuptools's fault

[JI Ioannidis]

I was getting the following build error on some machines, but not on others, and they were all running Ubuntu 16.04.1

File "/usr/lib/python2.7/dist-packages/setuptools/command/build_ext.py", line 175, in build_extension

    if ext._needs_stub:

AttributeError: Extension instance has no attribute '_needs_stub'

It turns out that the difference was that some had setuptools installed from apt, which was bringing in version 20 or so, and some had a modern version that I had installed with pip install.

The former failed, the latter succeeded.

I hope this saves somebody some hair-tearing.

I submitted an issue: https://github.com/grpc/grpc/issues/8004