Minimal acceptance tests for exporter

[natalieparellano]

Description

We have #467 for adding acceptance tests for the exporter. That issue intends for the tests for be comprehensive, which is a tall order. We should have very minimal acceptance tests for exporter that cover basic things, like:

• it works
• the output app image has the correct os / arch
• the output cache image has the correct os / arch

Proposed solution

We could copy / paste some setup from the existing restorer acceptance tests (e.g., related to the cache). We should assume that it's a very simple build and maybe it's the first build so we don't have to re-use layers.

Additional context

This will help #435

[natalieparellano]

Manually confirmed:

• When provided an arm64 image as its working image, the exporter on arm64 will output an arm64 image
• When creating a new cache image, the exporter on arm64 will create an image with empty arch; this image is pullable on an arm64 machine

Unknown:

• What happens when the run image provided is a manifest list?
• What happens when the cache image provided is a manifest list?

[natalieparellano]

Messy branch with minimal tests needed to release arm: https://github.com/buildpacks/lifecycle/compare/exporter-acceptance?expand=1