GitLab

dialing 4000 connections somehow keeps choking both travis and
jenkins. dialing this down to 500

This commit makes all network tests use ZeroLocalTCPAddress
as the initial peer address, and then relies on
net.ListenAddresses()

This should get rid of the tcp addr clash problems.

The net package is the next to move. It will be massaged
a bit still to fix the Network / "NetworkBackend" conflict.