log errors in pod package

@anthonybishopric 

Does this look like the right thing to do? I'm keeping the logging at the pod package level (we just want to know if big stuff like Install() or Launch() fail, with detailed error messages in the log message).

I also felt that the outer agent loop (preparer) should know whether a halt fully succeeded, even if we don't return an error. Maybe I should instead return a map of errors instead of a bool? LMK what you think
`pod.logLaunchableError(launchable, err)` for instance