Add Audit Scope Handler

This patch set adds audit scope mechanism.
It also removes host_aggregate field.

Change-Id: Ia98ed180a93fc8c19599735e2b41471d322bae9a
Partially-Implements: blueprint define-the-audit-scope

watcher/decision_engine/strategy/context/default.py

@@ -53,6 +53,8 @@ class DefaultStrategyContext(base.BaseStrategyContext):
 
         selected_strategy = strategy_selector.select()
 
+        selected_strategy.audit_scope = audit.scope
+
         schema = selected_strategy.get_schema()
         if not audit.parameters and schema:
             # Default value feedback if no predefined strategy