Auto merge of #3538 - mdr0id:mac_fix_local_rpctest, r=daira

Auto merge of #3538 - mdr0id:mac_fix_local_rpctest, r=daira

Update for Mac OS local rpc-tests

This PR is for #3341 .

The main issue is that ```#!/usr/bin/env python2``` is not valid on Mac. However, ```#!/usr/bin/env python``` is standard for Python2.7 interpreter link.

On a side note, pyflakes does a passive check on modules imported per some python file. This allows modules to be imported even if they do not exist on the current system (e.g. pyzmq, pybake2). Ultimately, the missing modules wont throw errors until ```rpc-test.sh``` calls that python file.

I sanity checked running this update on an Ubuntu 16.04 node, and the tests pass as expected (minus a known issue that is independent from this update). Also have updated the RTD documentation for the MacOS user guide procedure.