Add simple task affinity feature

 * This works only if we want to receive msg on
   one of all tagged nodes.
 * We should set 'host' parameter in executor
   section of our config for correct task affinity
   work.

Partially implements: blueprint mistral-task-executor-affinity

Change-Id: Ia7b529529695163ee1819fce47ac22fddce414fb
Merge "Add simple task affinity feature"