This PR changes the fingerprint handling of network interfaces that only
contain link local addresses. The new behavior is to prefer globally
routable addresses and if none are detected, to fall back to link local
addresses if the operator hasn't disallowed it. This gives us pre 0.6
behavior for interfaces with only link local addresses but 0.6+ behavior
for IPv6 interfaces that will always have a link-local address.
Fixes https://github.com/hashicorp/nomad/issues/3005
/cc diptanuc
This PR:
* Makes AWS network speeds more granular
* Makes `network_speed` an override and not a default
* Adds a default of 1000 MBits if no network link speed is detected.
Fixes#1985
