Tests: update randomization for ES 1.5.1
Tests: update randomization for ES 1.5.1

Elasticsearch version 1.5.1 was released today, so move to testing against
the release version and add 1.5.2-SNAPSHOT.

Original commit: elastic/x-pack-elasticsearch@36b502dbb1c733721a3c139b2ea482572278a3f9

vroyer/elassandra,nknize/elasticsearch,strapdata/elassandra,vroyer/elassandra,nknize/elasticsearch,gfyoung/elasticsearch,scorpionvicky/elasticsearch,robin13/elasticsearch,robin13/elasticsearch,scorpionvicky/elasticsearch,HonzaKral/elasticsearch,coding0011/elasticsearch,gingerwizard/elasticsearch,uschindler/elasticsearch,vroyer/elassandra,strapdata/elassandra,robin13/elasticsearch,gingerwizard/elasticsearch,gingerwizard/elasticsearch,GlenRSmith/elasticsearch,robin13/elasticsearch,uschindler/elasticsearch,gfyoung/elasticsearch,HonzaKral/elasticsearch,GlenRSmith/elasticsearch,uschindler/elasticsearch,gingerwizard/elasticsearch,uschindler/elasticsearch,gingerwizard/elasticsearch,GlenRSmith/elasticsearch,coding0011/elasticsearch,gfyoung/elasticsearch,scorpionvicky/elasticsearch,gfyoung/elasticsearch,nknize/elasticsearch,strapdata/elassandra,GlenRSmith/elasticsearch,coding0011/elasticsearch,nknize/elasticsearch,scorpionvicky/elasticsearch,scorpionvicky/elasticsearch,HonzaKral/elasticsearch,coding0011/elasticsearch,strapdata/elassandra,robin13/elasticsearch,gingerwizard/elasticsearch,nknize/elasticsearch,gingerwizard/elasticsearch,uschindler/elasticsearch,gfyoung/elasticsearch,GlenRSmith/elasticsearch,coding0011/elasticsearch,strapdata/elassandra,HonzaKral/elasticsearch