incomplete fix for exception handling in flushRotatedLogs method and need of ConcurrentList for rotatedLogChannels

[reddycharan]

BUG REPORT

1. Please describe the issue you observed:

As part of this bug https://issues.apache.org/jira/projects/BOOKKEEPER/issues/BOOKKEEPER-1044, following fix has been made cfe8bce but this seems to be an incomplete fix. If there is an exception while closing fileChannel (closeFileChannel(channel)) then it is not handled with this fix.

Also it would be much simpler to use some sort of ConcurrentList for rotatedLogChannels, since it would remove the need of guard of synchronization on EntryLogger/EntryLogManager instance and it would be much simpler to implement function which access / operate on rotatedLogChannels.

[reddycharan]

@sijie @eolivelli

[sijie]

@reddycharan is this issue fixed with your entry log manager changes?