Initial execution of parallel engines can be racey

[Dave Walker]

When running multiple watcher engines in parallel (ie, via automated HA deployment), the initial run can create multiple duplicate Goals and Strategies.

For example:
+--------------------------------------+----------------------+----------------------+
| UUID | Name | Display name |
+--------------------------------------+----------------------+----------------------+
| 55211ddd-e9a5-4105-b8e8-c177c0de59fa | server_consolidation | Server consolidation |
| b084a6c7-e03e-4ef6-ba72-10e493ba2b6e | dummy | Dummy goal |
| 2ff77cc0-0f20-4fd7-a739-4346a044a961 | thermal_optimization | Thermal optimization |
| 542de4f0-73c7-461d-b4e3-b8dbe808e0d6 | thermal_optimization | Thermal optimization |
| f78952c5-294b-4f33-9fb7-7b2f4d7494a8 | unclassified | Unclassified |
| 6beb2ff1-fffb-488b-a7db-92615761fe13 | unclassified | Unclassified |
| 45a9d181-0641-451e-97b5-0f705fd9c16f | workload_balancing | Workload balancing |
| aa619ddd-7265-4857-a57e-e3776b668a5c | workload_balancing | Workload balancing |
+--------------------------------------+----------------------+----------------------+

This has bad consequences, such as:
2016-07-04 17:22:41.053 1 CRITICAL python-watcher [req-b99b79f4-2b24-4dab-a1be-c0c90713b726 - - - - -] MultipleResultsFound: Multiple rows were found for one()
2016-07-04 17:22:41.053 1 ERROR python-watcher Traceback (most recent call last):
2016-07-04 17:22:41.053 1 ERROR python-watcher File "/var/lib/kolla/venv/bin/watcher-decision-engine", line 10, in <module>
2016-07-04 17:22:41.053 1 ERROR python-watcher sys.exit(main())
2016-07-04 17:22:41.053 1 ERROR python-watcher File "/var/lib/kolla/venv/lib/python2.7/site-packages/watcher/cmd/decisionengine.py", line 43, in main
2016-07-04 17:22:41.053 1 ERROR python-watcher syncer.sync()
2016-07-04 17:22:41.053 1 ERROR python-watcher File "/var/lib/kolla/venv/lib/python2.7/site-packages/watcher/decision_engine/sync.py", line 119, in sync
2016-07-04 17:22:41.053 1 ERROR python-watcher self.strategy_mapping.update(self._sync_strategy(strategy_map))
2016-07-04 17:22:41.053 1 ERROR python-watcher File "/var/lib/kolla/venv/lib/python2.7/site-packages/watcher/decision_engine/sync.py", line 167, in _sync_strategy
2016-07-04 17:22:41.053 1 ERROR python-watcher strategy.goal_id = objects.Goal.get_by_name(self.ctx, goal_name).id
2016-07-04 17:22:41.053 1 ERROR python-watcher File "/var/lib/kolla/venv/lib/python2.7/site-packages/watcher/objects/goal.py", line 116, in get_by_name
2016-07-04 17:22:41.053 1 ERROR python-watcher db_goal = cls.dbapi.get_goal_by_name(context, name)
2016-07-04 17:22:41.053 1 ERROR python-watcher File "/var/lib/kolla/venv/lib/python2.7/site-packages/watcher/db/sqlalchemy/api.py", line 432, in get_goal_by_name
2016-07-04 17:22:41.053 1 ERROR python-watcher return self._get_goal(context, fieldname="name", value=goal_name)
2016-07-04 17:22:41.053 1 ERROR python-watcher File "/var/lib/kolla/venv/lib/python2.7/site-packages/watcher/db/sqlalchemy/api.py", line 421, in _get_goal
2016-07-04 17:22:41.053 1 ERROR python-watcher fieldname=fieldname, value=value)
2016-07-04 17:22:41.053 1 ERROR python-watcher File "/var/lib/kolla/venv/lib/python2.7/site-packages/watcher/db/sqlalchemy/api.py", line 243, in _get
2016-07-04 17:22:41.053 1 ERROR python-watcher obj = query.one()
2016-07-04 17:22:41.053 1 ERROR python-watcher File "/var/lib/kolla/venv/lib/python2.7/site-packages/sqlalchemy/orm/query.py", line 2727, in one
2016-07-04 17:22:41.053 1 ERROR python-watcher "Multiple rows were found for one()")
2016-07-04 17:22:41.053 1 ERROR python-watcher MultipleResultsFound: Multiple rows were found for one()
2016-07-04 17:22:41.053 1 ERROR python-watcher