RATIS-1879. Handle RaftLog corruption when unsafe flush is enabled.

[szetszwo]

See https://issues.apache.org/jira/browse/RATIS-1879

[SzyWilliam]

Thanks @szetszwo very much for the patch! I'll use the patch to restart and see if we can fix it later on.

[szetszwo]

@SzyWilliam , as @OneSizeFitsQuorum mentioned in RATIS-1879. We already have WARN_AND_RETURN corruption policy. We does not seem to need this anymore.

[SzyWilliam]

@szetszwo Thanks a lot! I was still worrying about this issue yesterday since it turned out that our user turned off the unsafeFlush and I made a mistake when firing a issue. The corruption problem may happen whether we enable unsafeFlush or not.
Now that I know CorruptionPolicy and it perfectly meet our needs.
Thanks @szetszwo @OneSizeFitsQuorum again!

[OneSizeFitsQuorum]

@szetszwo it looks like you already addressed the issue reported by Ozone four years ago, which is really cool. Thank you for your thorough work!!!

[szetszwo]

Closing this since the problem is already fixed.