Parser doc selection logging

Two changes:

I noticed that if a parse succeeds you can see the config document used in the log via the `DEBUG habitat.parser MainThread: Parsed data: {` line, but it's not shown for failed parses. The second commit adds that.

I wanted to quickly check the logging output so looked for something that tested _get_config  without a provided config - couldn't find it, so added it. It was tested already (indirectly) by test_parse, but I figured since some of the other tests mock _get_config out, why not