Add service supervisor

This patch set adds supervisor mechanism for Watcher services
to get ability to track states.

Partially-Implements: blueprint watcher-service-list
Change-Id: Iab1cefb971c79ed27b22b6a5d1bed8698e35f9a4

etc/watcher/policy.json

@@ -37,5 +37,9 @@
 
     "strategy:detail": "rule:default",
     "strategy:get": "rule:default",
-    "strategy:get_all": "rule:default"
+    "strategy:get_all": "rule:default",
+
+    "service:detail": "rule:default",
+    "service:get": "rule:default",
+    "service:get_all": "rule:default"
 }