Do not ignore ConnectTransportException for shard replication operations

A ConnectTransportException on replicating an index operation should fail the replica shard.

This case came out of the `improve_zen` branch for index requests that are mid-flight while partitioning is forced.
@martijnvg I'm trying to think of the best way to verify where the document exists on both shards, I guess just get the document count from the stats for each shard? Checking that the indexing op doesn't fail is kind of redundant for this, so it could be entirely removed.