Enhancement: generate openstack keypair on create

It would be a good idea for kitchen-openstack driver to generate a temporary openstack keypair used for instance creation and remove it on kitchen destroy.

[jjasghar]

This would require a creation of a new tenant and quite a bit of engineering. It sounds great, and I'd love to see someone put the time in for this, but it's out of scope for basic usage.

Thanks for the suggestion though!