log whole response body on error to give a chance to understand a reason

[sitano]

usually response for /status? kind of requests would contain a description of why it failed

[agentzh]

@sitano Thanks for the patch and I understand this is more useful. However, your change breaks the existing test suite. I'm getting these failures:

https://gist.github.com/agentzh/adf13526aa1625d7e50b

Will you update the test suite accordingly as well? Thanks!