Add user/password for elastic 5.5.1 X-Pack

[yaneclev]

It seems the client don't support authentication.....

[tanhaipeng]

please confirm the client is or not support authentication, thx

[neilcook]

BTW this is merged into my fork of this branch. Plus a small fix.

[onlonely]

No examples found.
Haven't merged into the current trunk yet?

[neilcook]

It's merged in my fork, which is now the only maintained version of this repo that I know of. It also supports TLS.

https://github.com/PowerDNS/elasticsearch-lua