Fix IOError on WAL write doesn't propagate to write group follower

Fix IOError on WAL write doesn't propagate to write group follower

Summary:
This is a simpler version of #3097 by removing all unrelated changes.

Fixing the bug where concurrent writes may get Status::OK while it actually gets IOError on WAL write. This happens when multiple writes form a write batch group, and the leader get an IOError while writing to WAL. The leader failed to pass the error to followers in the group, and the followers end up returning Status::OK() while actually writing nothing. The bug only affect writes in a batch group. Future writes after the batch group will correctly return immediately with the IOError.
Closes https://github.com/facebook/rocksdb/pull/3201

Differential Revision: D6421644

Pulled By: yiwu-arbug

fbshipit-source-id: 1c2a455c5b73f6842423785eb8a9dbfbb191dc0e