R1:e41c25de5050

Support multiple fulltext search clusters with 'cluster.search' config

Summary:
The goal is to make fulltext search back-ends more extensible, configurable and robust.

When this is finished it will be possible to have multiple search storage back-ends and
potentially multiple instances of each.

Individual instances can be configured with roles such as 'read', 'write' which control
which hosts will receive writes to the index and which hosts will respond to queries.

These two roles make it possible to…