Verify crawler performance and find best parameter

[ddio]

As a crawler engineer, I want to know appropreciate minuteago setting, so

1. Crawler can perform all its work in minuteago 24 hours a day, 7 days a week.
2. Reduce target website #request at best
3. The higher update frequency the better

Acceptance Criteria

1. All of goal mentioned above
2. Provide a mechanism to ensure crawler won't be executed simultaneously even when it take longer than minuteago

[ddio]

Action Items

1. Detail test plan
2. Implement job collision avoidance alg.