Adds a validation for plugins script to check if java is set
Adds a validation for plugins script to check if java is set

This does the same validation as in elasticearch bin script

strapdata/elassandra-test,baishuo/elasticsearch_v2.1.0-baishuo,baishuo/elasticsearch_v2.1.0-baishuo,strapdata/elassandra-test,baishuo/elasticsearch_v2.1.0-baishuo,strapdata/elassandra-test,strapdata/elassandra-test,baishuo/elasticsearch_v2.1.0-baishuo,baishuo/elasticsearch_v2.1.0-baishuo,strapdata/elassandra-test,baishuo/elasticsearch_v2.1.0-baishuo,baishuo/elasticsearch_v2.1.0-baishuo,strapdata/elassandra-test,strapdata/elassandra-test