Authorization context propagation for service separation - EUCA-8712

Authorization context information can now be propagated between service
and backend using the new BaseCallerContext. Policy condition keys can
now be tagged with the new ReceivingHost evaluation constaint to force
early evaluation and propagation to the backend service when using
AsyncRequests.sendSyncWithCurrentIdentity.

There is a new AuthContext and refactored AuthEvaluationContext for use
with Permissions/PolicyEngine allowing propagation of authorization
context information from the request Context to authorization APIs.

EUCA-8712