Loosen docker daemon requirement for running tests

Today most levels of test in this repo require that docker is installed available. It would be ideal to loosen this some by allowing for additional container runtimes for test fixtures or in some cases looking for opportunities to eliminate the need for a container runtime to generate test fixtures.

This would have been helpful for https://github.com/anchore/syft/pull/447 .

Start by reviewing the repository's test setup and how Docker is required for test fixtures. Use anchore/syft#447 as context for the limitation described in this issue. Done would mean tests can use additional container runtimes or avoid a container runtime for suitable fixtures, with the affected test levels still passing.

Written by the indexing model from the issue text.