RATIS-2151. TestRaftWithGrpc keeps failing with zero-copy.

[szetszwo]

RATIS-2151

This is to fix the following problems described in #1156
3. GrpcClientProtocolService.UnorderedRequestStreamObserver.processClientRequest(..) should use try-finally.
4. GrpcLogAppender.appendLog(..) calls release() incorrectly for exception.
6. LogSegment cache can release an entry multiple times.
7. LogSegment.loadCache(..) should call retain() for cache hit.
8. SegmentedRaftLog.retainLog(..): between getting the entry and calling retain(), the entry can be released. The "fail to retain" exception, if there is any, can be ignored since It is the same as a cache miss. See #1153
9. SegmentedRaftLog.retainEntryWithData(..) should release for exception.
10. Test bug: the log entries stored in SimpleStateMachine4Testing can be released.
11. LogSegment: New entries can be added after EntryCache is closed.
13. SegmentedRaftLogWorker should clean up unfinished tasks in the queue after stopped running.

[szetszwo]

@duongkame , @133tosakarin , @OneSizeFitsQuorum , @adoroszlai , please take a look.

[adoroszlai]

Thanks @szetszwo for the patch, LGTM.

[szetszwo]

@adoroszlai , could you approve this? I guess no one else will review this.

[szetszwo]

@adoroszlai , thanks a lot for reviewing and approving this!