652 - Bump L0 API instance to t3.small

[alqvia]

What does this pull request do?
Fixes #652

How should this be tested?
Build l0-setup and run the following against the preprod AWS account:

./l0-setup init --docker-path=/path/to/my/docker_config uswest2dev
./l0-setup plan uswest2dev > ~/plan.log
./l0-setup apply uswest2dev
./l0-setup destroy uswest2dev

NOTE: For init, you need to point to the following module on your machine, e.g. /Users/<myusername>/go/src/github.com/quintilesims/layer0/setup/module

This has been tested as specified above and successfully created the L0 API.

Checklist

• [ x] Unit tests
• Smoke tests (if applicable)
• System tests (if applicable)
• Documentation (if applicable)

closes #652

[alqvia]

Also, we've had similar issues w/ us-west-2d and t2 Chunnel instances, which were also fixed by moving up to the next gen t3 instance.