Non-Blocking Connection and Timeout Support

[bufferx]

Issue

• The Blocking IO Connection will causing that the tornado service can not respond new HTTP Request, when MongoDB server goes down(Error: no route to host).

New Feature

• create Non-blocking connection to mongodb service, support for connection timeout and request timeout, when using tornado as the Async Backend
• add life time for long connection

Refrence

• Inspiration from tornado.simple_httpclient._HTTPConnection

[bufferx]

@jehiah hey jehiah, do you have plan to review and merge this patch soon? Thanks.