Zap async test fix

I was looking over the reset builds on Travis and noted this error.
  https://travis-ci.org/JustinTulloss/zeromq.node/jobs/36125434

start() will run multiple times concurrently so the inproc name needs to be unique to avoid the EADDRINUSE error on bindSync().

To fix I added a counter to append to the inproc name to force it to be unique in the context.
 
Testing will suck as this error is hard to reproduce.