Replace RabbitMQ with Amazon SQS

[infinitewarp]

kill the rabbit https://youtu.be/Yxiv3CBMS4M

https://github.com/cloudigrade/cloudigrade/issues/296

This PR does a few things:

• make environment variable names more generic so it doesn't look like we need RabbitMQ
• drop the RabbitMQ container from docker-compose.yml
• updates README with new instructions for running locally with docker compose

[codecov[bot]]

Codecov Report

Merging #12 into master will not change coverage. The diff coverage is 100%.

@@          Coverage Diff          @@
##           master    #12   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files           2      2           
  Lines         204    204           
  Branches       10     10           
=====================================
  Hits          204    204

Impacted Files	Coverage Δ
houndigrade/cli.py	100% <100%> (ø)	:arrow_up:

---

Continue to review full report at Codecov.

Legend - Click here to learn more Δ = absolute <relative> (impact), ø = not affected, ? = missing data Powered by Codecov. Last update 10c3782...549b23f. Read the comment docs.

[infinitewarp]

demo: https://asciinema.org/a/185696