#357 Wait for eth0 to be up before starting docker - borrow existing code

Took code from tc-config which waits for dhcp to complete.  This version doesn't ping, but you could ping the DNS server (10.0.2.3) which I think only exists if you have nat dns host resolver enabled or 10.0.2.2 (does that always exist?)
This, tied with a change in boot2docker-cli which would create the VM with the nat dns host resolver (that I haven't yet codified) will make sure dns for containers is the same as the host dns.  I tested this manually :(