make unit tests quiet

[flavorjones]

The test suite has always been very noisy. This PR:

• captures the logs of the test webrick server (instead of stdout)
• captures the logs of the test recipes (instead of stdout)
• wraps GPG errors up into the exceptions (instead of stderr)
• uses the recipe logger in a few places that were doing raw puts
• addresses a few minitest deprecation warnings
• removes some debug messages left in the tests
• shushes an uninitialized-ivar warnings on older rubies
• moves test:unit rake task to Rake::TestTask

Thanks to @postmodern for pointing out how noisy the logs were where I had become immune to it.