EUCA-8127: ELB policy implementation and session stickiness front-end
The session stickiness and SSL termination uses policy API to tag attributes to specific ELBs.
For example, 'CookieName' is a policy attribute attached to an ELB that governs the ELB's behavior around app-generated cookies.
This commit implements the policy APIs (create/delete/describe), and the Create(App/LB)CookieStickinessPolicy.
The change does not include actual enforcement of the session stickiness by HAProxy.