Openstack cloud

This version supports appscale on Openstack. It initializes the instances automatically. There is no need to add the instances addresses manually. TODO: Check auto-scalling (I believe it works since Appscale measures the HAProxy, not the telemetry module of Openstack). 

Notice: the image id is the AWS image-id, not the Openstack id. The image id format is: ami-0000000X