splitVector can't be run against secondary

Hi,

I am working with the mongo hadoop connector on a replica set and I want to use it on a secondary machine. The mongo hadoop driver runs `splitVector` (https://github.com/mongodb/mongo-hadoop/blob/master/core/src/main/java/com/mongodb/hadoop/splitter/StandaloneMongoSplitter.java#L94). However, splitVector can't be run against a secondary machine:

MongoDB Enterprise test:SECONDARY> db.runCommand({splitVector: "test.testData", "keyPattern": {_id: 1}, maxChunkSize: 1})

{ "ok" : 0, "errmsg" : "not master", "code" : 10107 }

Can someone explain the reason for this? It would be great if we could use the mongo hadoop connector on a non-primary machine and this appears to be a blocking issue for that to happen.

Thanks,
Ben