Fix bug env node and update conf with the good script name

Yes. There are two things.
- Fix bug node js
- Add item `dbsize`: in nodejs file and in template. `dbsize` content the number of keys. The same result of `redis-cli ... dbsize`
For the template, I just import your file, add the new item and export.
(It was on a zabbix 2.2.6.)

I should have done 2 pull request separated.. Sorry