Summary:
This diff does 3 things:
Expose TransactionID so that we can identify transactions when we retrieve locking and lock wait information. This is exposed as `Transaction::GetID`.
Expose lock state information by locking all stripes in all column families and copying their contents to a data structure. This is exposed as `TransactionDB::GetLockStatusData`.
Adds support for tracking the transaction and the key being waited on, and exposes this as `Transaction::GetWaitingTxn`.
Test Plan: unit tests
Reviewers: horuff, sdong
Reviewed By: sdong
Subscribers: vasilep, hermanlee4, andrewkr, dhruba
Differential Revision: https://reviews.facebook.net/D64413