Dockerfile for terraform image with Redshift provider

[paranoidd]

This PR will:

• Add Dockerfile with compiled Redshift provider;
• Add 'docker' make target

Asked by @frankfarrell in #33 - I can't provide anything from my workplace, so I decided to write custom Dockerfile that builds the provider into official hashicorp terraform image.

Hope this will be useful, and in case of questions, do not hesitate to ask them :-)

[frankfarrell]

Awseome thanks!
The only think I would add is a note on how to use it in the README.
Is that ok if I publish it to my dockerhub, or do you want to push to yours?

Cheers