This adds a remote option to reindex that looks like
```
curl -POST 'localhost:9200/_reindex?pretty' -d'{
"source": {
"remote": {
"host": "http://otherhost:9200"
},
"index": "target",
"query": {
"match": {
"foo": "bar"
}
}
},
"dest": {
"index": "target"
}
}'
```
This reindex has all of the features of local reindex:
* Using queries to filter what is copied
* Retry on rejection
* Throttle/rethottle
The big advantage of this version is that it goes over the HTTP API
which can be made backwards compatible.
Some things are different:
The query field is sent directly to the other node rather than parsed
on the coordinating node. This should allow it to support constructs
that are invalid on the coordinating node but are valid on the target
node. Mostly, that means old syntax.
b3c015e2bb