percolate REST API should support source parameter

As stated in documentation, we should support `?source=` parameter in percolate REST operations.

This is how to reproduce it:

```sh
curl -XDELETE "http://localhost:9200/test"

curl -XPUT "http://localhost:9200/test/.percolator/1" -d'
{
"query" : {
"match" : {
"foo" : "bar"
}
}
}'

# This one works
curl -XPOST "http://localhost:9200/test/message/_percolate" -d '{
"doc" : {
"foo" : "bar is in foo"
}
}'

# This one gives: BroadcastShardOperationFailedException[[test][2] ]; nested: PercolateException[failed to percolate]; nested: ElasticsearchIllegalArgumentException[Nothing to percolate];
curl -XGET "http://localhost:9200/test/message/_percolate?source=%7B%22doc%22%3A%7B%22foo%22%3A%22bar%20is%20in%20foo%22%7D%7D"
```

Closes #4903.