tests: patcher_test: let Popen search for `true` in PATH
tests: patcher_test: let Popen search for `true` in PATH

As Edward George reported in https://github.com/eventlet/eventlet/pull/3
There is no /bin/true on Darwin, it is in /usr/bin/true instead.
So we use the fact that Popen() calls execvp(3) which searches for file in PATH.

collinstocks/eventlet,lindenlab/eventlet,collinstocks/eventlet,tempbottle/eventlet,tempbottle/eventlet,lindenlab/eventlet,lindenlab/eventlet