Add testing infrastructure

[whd]

Reaper should have some test coverage, using the standard testing package and go test for unit tests. There may be some difficulty in mocking the API, which needs to be investigated. Hashicorp code is probably a good resource for how to test the AWS SDK components of the program. It may additionally be prudent to have a heavier-handed integration / validation test that actually spins up AWS resources to test actual resource destruction and modification.

It is possible to generate similar output to what the API produces by creating structs manually, but it would be easier and nicer to be able to load in the resources from a serialized representation.

We should set up Travis to run these tests on PRs. go vet and -race should be integrated.