Print package downloads except background updater

Before, there were some random contexts (like 'test-packages') which
didn't print downloads. Now, the default is printing, and the exception
is the automatic background updater.

(Some of these bulk contexts should probably set silent and print their
own progress bar.  And maybe even do paralellism...)

Generally clean up the tropohouse.maybeDownloadPackageForArchitectures
interface. Change it to take options, remove the vestigial return
value (though really, there needs to be better error handling...)