Automatically check that network route to boot2docker VM is set up in init.sh

[JoshRosen]

We should automatically check that container IP addresses are properly routed to the boot2docker VM before running tests. If this is misconfigured, then tests can mysteriously hang or fail, which can be confusing to new users.

This might be pretty simple; we might be able to use a route or traceroute command to check for this in the init.sh script.