Upgrade GRPC to v1.7.1

I’ve always been uncomfortable with multiple tests (and hence multiple servers) sharing the same unix socket. Well, in grpc 1.7, this has stopped working, and is causing race conditions between the shutdown of one test and the startup of the next (using the same socket)

The workaround has been to change all the tests so that each server that gets started has a unique socket path.

This is simple to do, but is a lot of change. My apologies if this results in merge conflicts in your code, but it seems to be the only workaround (and imho, one less bit of technical debt)