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


Use .format for constructing strings. See: https://github.com/AppScale/appscale/pull/1556/files#diff-6c7907b47e9a5557c1e55b4d7ba55cc2R134