Include error body on Bad HTTP error code on wrong logging level

[philwebb]

See issue #8798 and PR #8813 and this comment:

... the HTTP 400 response does not contain a body anymore which makes it impossible to understand the reason why the request has failed.

IMO, the error response should contain a reason for the error, similar to the message of the initial HTTP 500 error.

[eddumelendez]

@philwebb should it be based on branch 1.5.x or master?

[philwebb]

Closing in favor of PR #10588. Thanks again @eddumelendez !!