Enable architecture specific dependencies

[c0d1ngm0nk3y]

fixes #618

Summary

When looking for an dependency, the architecture is taken into account. The default architecture (if not provided by a dependency is "amd64" to ensure backwards compatibility. The architecture to look for is taken from the system or an env variable BP_ARCH to enable unit testing.

Use Cases

Dependencies for several architectures (e.g. "arm" and "amd64")

Checklist

• I have viewed, signed, and submitted the Contributor License Agreement.
• I have linked issue(s) that this PR should close using keywords or the Github UI (See docs)
• I have added an integration test, if necessary.
• I have reviewed the styleguide for guidance on my code quality.
• I'm happy with the commit history on this PR (I have rebased/squashed as needed).