Added a Dockerfile to create Chef language pack

We need Chef language pack with chef specific
testing tools installed on it.
This patch provides a Dockerfile to create such a LP.

Implements: blueprint chef-language-pack

https://blueprints.launchpad.net/solum/+spec/chef-language-pack

Change-Id: I8d4ee18efb4ea1b144c5f4583922d09795146c27
Merge "Added a Dockerfile to create Chef language pack"