Allow some tests to create more then 1 shard.

This is needed when we want to test things with a routing param.
Add test for delete by query calls with request params
Allow for request params in delete by query calls

Delete by query calls allows for optional request params to tune things
like routing, replication and consistency.

http://www.elasticsearch.org/guide/en/elasticsearch/reference/current/docs-delete-by-query.html#delete-by-query-parameters
Update changelog
Add optional  param to BaseAggregationTest::_createIndex()
Merge pull request #573 from xyu/delete-by-query-params

Allow for request params in delete by query calls