Chore: Better error messages on download of archetype.

[ryan-roemer]

In downloading / extracting an archetype, we go through creating a temp directory, a process spawn (npm pack), ungzip, untarring to the temp directory and walking that file path. There's a lot that can go wrong with very terse / hard-to-understand error messages.

Task:

• Review and add error wrappers to make captured errors much more accesible.
• Add information to error about where things went wrong.

Scenarios:

• Archetype doesn't have init.js
• Archetype doesn't have init/

[ryan-roemer]

Some of this (like npm pack process errors) is better now. Probably just a simple edit + looking at code coverage report of error paths not handled in tests / messages asserted.