Add support for deploying Amphora in overcloud

Octavia introduces the concept of "amphora" or LBaaS workers to be deployed as VM instances in the overcloud. The final stage of providing complete "out of the box" support for Octavia implies construction and deployment of amphora images, configuration of required neutron networks in the overcloud and determining requirements for specialized roles (if necessary) for supporting amphorae instances (i.e. do we want them to run on general compute nodes or are we defining a new role for them)