Renamed Status to State

As we can see in the codebase, we have 3 "Status" enums which are
located at:

- watcher/objects/action.py
- watcher/objects/action_plan.py
- watcher/objects/audit.py

So I renamed them from "Status" to "State" to be consistent with
the DB schema.

Change-Id: If3d180c9daba6ae9083775ad6813aa4c21763dbf
Closes-Bug: #1522733

watcher/objects/action.py

@@ -22,7 +22,7 @@ from watcher.objects import base
 from watcher.objects import utils as obj_utils
 
 
-class Status(object):
+class State(object):
     PENDING = 'PENDING'
     ONGOING = 'ONGOING'
     FAILED = 'FAILED'