Check and fix percolate Java API
Sounds like http://www.elasticsearch.org/guide/reference/java-api/percolate/ is wrong.

```java
//This is the query we're registering in the percolator
QueryBuilder qb = termQuery("content", "amazing");

//Index the query = register it in the percolator
client.prepareIndex("_percolator", "myIndexName", "myDesignatedQueryName")
    .setSource(qb.buildAsBytes())
    .setRefresh(true) //Needed when the query shall be available immediately
    .execute().actionGet();
```

Should be:

```java
//This is the query we're registering in the percolator
QueryBuilder qb = termQuery("content", "amazing");

//Index the query = register it in the percolator
client.prepareIndex("_percolator", "myIndexName", "myDesignatedQueryName")
    .setSource(jsonBuilder().startObject()
                        .field("query", qb)
                        .endObject())
    .setRefresh(true) //Needed when the query shall be available immediately
    .execute().actionGet();
```

Closes #449.