builder/virtualbox: Add `hard_drive_interface` option

Otherwise we get stuck in a long loop. Whoops.

See comment.

Most APIs return "has a pending event" but power off seems to return
"already a pending event". WTF. Also, just wtf at the DigitalOcean API.
I can't wait until they change their english and this breaks. Because
it is definitely going to happen, and it's going to be such a fun time.

/cc @pearkes - I hate this thing.

Add make format information in the README.

builder/openstack: allow project to be specified

It isn't actually optional, according to the spec

builder/openstack: Support IPv6 access address for Openstack

builder/vmware: fix typo

s/Detatching/Detaching/

builder/openstack: Increase default SSH timeout from 1m -> 5m

Many cloud providers have a minimum charge of 1 hour, and if there are DNS problems we can hit the 1 minute timeout easily.

Waiting five minutes gives more of a margin of error.