update API: set groovy as language
update API: set groovy as language

ES 1.3 still uses MVEL as the default scripting language. We enforce
using groovy in the tests.

olivere/elastic,hustbill/elastic,yonglehou/elastic,TinLe/elastic,grafov/elastic,olivere/elastic,gmack/elastic,guilherme-santos/elastic,CptJason/elastic,mruse/elastic,dorsha/elastic,antonikonovalov/elastic,harrisonchen/elastic,guilherme-santos/elastic,nizsheanez/elastic,grafov/elastic,cep21/elastic