Add fluxfw-gcp

[wkharold]

This pull request adds scripts and Terraform configs for the flux-framework on GCP.

It consists of:

• a directory img containing the scripts necessary to build flux-framework images for GCP
• a directory tf containing Terraform config modules that can be used to deploy flux-framework on GCP
• a directory tf/examples containing concrete examples of flux-framework deployments on GCP

[mmm]

couple of general notes:

• I'm not sure the ramifications for having multiple LICENSE files within a repo... might be better to just have the top-level one so we prevent skew over time? Dunno
• I think it's a good idea to add a link from the top-level README.md... customers often end up there inadvertently. I was thinking we could do flat top-level example folders, but then "organize" any of them into groups of examples or related content or other stuff simply from the links in the top-level README.md. Dunno

Nothing important to address now... just putting the thoughts out there: @wkharold @jrossthomson