Add debug logging

[c0d1ngm0nk3y]

see #439

Summary

Added some debug logging for checking if the node layer can be reused from cache.

Use Cases

Some debug information about why the node layer was not reused might be interesting in certain situations.

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).

[c0d1ngm0nk3y]

@sophiewigmore Did you had specific debug messages in mind that would be useful to have?

[sophiewigmore]

@c0d1ngm0nk3y not particularly, we haven't standardized what types of things we want in our debug logs, or how they should be structured yet. I hope to do that at some point soon.

In general, the types of things that I linked to in the issue from the MRI buildpack are definitely along the lines I was thinking - information about the installation path, source URI, anything that would help a user out understanding how Node is being installed in the event something went wrong.

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