update thrift to use managed connection

update thrift to use managed connection

Summary:
Use the new managed connection code in folly.  Cleans things up a fair bit

The only catch was the current ConnectionManager code uses raw pointers, thrift expects shared_ptr so the request object can keep the channel around until the requests are finished

Test Plan: fbconfig -r thrift/lib/cpp2; fbmake runtests

Reviewed By: afrind@fb.com

Subscribers: trunkagent, njormrod, doug, fugalh, alandau, bmatheny, dcsommer, afrind

FB internal diff: D1519923

Tasks: 5002343