Added new private_ip compute_options attribute.a

with_fog_provisioner :private_ip => true

This will enable you to connect to a private ip address instead of
public. This feature adds support for connecting to VPC's that do not
allow remote connections.
Updated private_ip variable to use_private_ip_for_ssh.

with_fog(_ec2)_provisioner :use_private_ip_for_ssh => true
Merge pull request #23 from xorl/private_ip

Added new private_ip compute_options attribute.