https://blueprints.launchpad.net/octavia/+spec/anti-affinity
Added a new column in lb table for server group id;
Added a new task in compute tasks for creating server group;
Added a new task in dtabase tasks to update server
group id info for lb;
Add server group id in create method in nova driver to support
anti-affinity when creating compute instance
Change-Id: If0d3a9ba1012651937a2bda9bc95ab4f4c8852d5