Make LedgerMetadata Immutable

[ivankelly]

JIRA: https://issues.apache.org/jira/browse/BOOKKEEPER-822

Reporter: Ivan Kelly @ivankelly

Mutable metadata has been a very rich source of bugs. There are multiple processing modifying for rebuilding ensembles, closing, fencing, autorecovery etc.

The local metadata should be a mirror of the metadata in zookeeper. So we should only modify the local metadata as a whole. The first part of this is making it immutable, so that it can only be modified with a builder.

Comments from JIRA

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Ivan Kelly 2017-10-09T09:28:33.199+0000

I think this is already done, but moving over to gh anyhow to verify.

[ivankelly]

WIP patch from 4 years ago.
ivankelly@8531463

[ivankelly]

Dupe of #281