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.

We still prefer the IPv4 address, but if there is an IPv6 address and no IPv4 address, use IPv6.

communicator/ssh: If PKCS1 parsing of the SSH key fails, try PKCS8

builder/openstack: If no image is generated, just return nil 

This mirrors what is done in other providers e.g. Amazon providers