Print a user-friendly error on initial connection failures

[etremel]

When Derecho runs on a machine with multiple network interfaces, it might automatically select the wrong one. If this happens, and it can’t connect to the remote machine, rather than giving a sensible error message it emits a confusing and strange error message (most likely caused by a failed attempt to parse a length-0 or even length -1 packet) and crashes. Since machines with multiple network interfaces are fairly common, we should print a more readable error message when this happens.