ServerRecheckCapture module

ServerRecheckCapture module

Summary:
This is the first take at recording the recheck inputs and setting up the replay environment based on one of those inputs.

The recording part captures the following after a recheck
- the changed files (paths and contents)
- the list of rechecked files (may not correspond to the fanout of the changed files as some rechecks are interrupted
- the errors produced by the recheck
- the merge base
- the recheck ID (for record keeping)

To restore the environment for recheck replay, the setup function does this:
- checks out the WWW repo to the merge base of the captured recheck
- applies the changes based on the changed file paths and contents
- writes the list of files to recheck into the fanout input file
- writes the expected errors in the JSON format into the expected errors file

Reviewed By: yinghuitan

Differential Revision: D20399898

fbshipit-source-id: 1f23222d86c80d80233a6049e9ecfee7092b2763