Check if byte strings are properly encoded in UTF-8

[isbm]

Sometimes 3rd party packages contains broken UTF-8 strings. This renders JSON output crash (although works on STDOUT and YAML). This PR fixes this problem and logs the error log about bad package.

[cachedout]

Thanks for sending this in @isbm

Could you please clarify what you mean by "broken UTF-8"? If those strings are just simply not UTF-8 and the underlying package manager supports them, it seems like we should try to as well. Thoughts?

[isbm]

@cachedout Well, some 3rd-party packagers entering, say, German umlauts or something else (Kanji?) and those symbols aren't properly converted or weren't properly stored (wrong editor, locale etc). Often it happens in the "Description" and "Summary" fields of the package. We also found few packages in our codebase this way. So in order to hunt all them down, prevent them in a future and ask maintainer to fix it, this PR helps to do so. However, typical API user will just get a description as is (just without these symbols).

I hope it makes sense.

[cachedout]

@isbm Sounds good. Thanks for the clarification.