Add support for setting JAVA_HOME to the `elasticsearch-env.sh.rb` template
Add support for setting JAVA_HOME to the `elasticsearch-env.sh.rb` template

If the `node.elasticsearch.java_home` attribute is set, it will be printed
as the JAVA_HOME environment variable in the `elasticsearch-env.sh.rb` template.

Closes #51

spuder/cookbook-elasticsearch,nbudin/cookbook-elasticsearch,gilt/cookbook-elasticsearch,nbudin/cookbook-elasticsearch,gouketsu/cookbook-elasticsearch,bavardage/cookbook-elasticsearch,nbudin/cookbook-elasticsearch,gilt/cookbook-elasticsearch,vacay/vcy-elasticsearch,gilt/cookbook-elasticsearch,gouketsu/cookbook-elasticsearch,zzugg/cookbook-elasticsearch,spuder/cookbook-elasticsearch,zzugg/cookbook-elasticsearch,michaeld/elasticsearch-cookbook,vacay/vcy-elasticsearch,gouketsu/cookbook-elasticsearch,spuder/cookbook-elasticsearch,GemHQ/cookbook-elasticsearch,paulczar/cookbook-elasticsearch,vacay/vcy-elasticsearch,zzugg/cookbook-elasticsearch