MultiPercolateRequest breaks when setting Routing

[justjico]

Edit test:
https://github.com/elasticsearch/elasticsearch/blob/master/src/test/java/org/elasticsearch/percolator/MultiPercolatorTests.java

        MultiPercolateRequestBuilder builder = client().prepareMultiPercolate();
        int numPercolateRequest = randomIntBetween(50, 100);
        for (int i = 0; i < numPercolateRequest; i++) {
            builder.add(
                    client().preparePercolate()
                            .setGetRequest(Requests.getRequest("test").type("type").id("1"))
                            .setRouting("test")
                            .setIndices("test").setDocumentType("type"));
        }

        MultiPercolateResponse response = builder.execute().actionGet();

[clintongormley]

@martijnvg could you look at this one please?