Implement debug logging for responses

In production code, we should never call end() on a response twice.  In
practice there are a lot of cases where this happens, and while it's
handled gracefully, it's incorrect.  This adds error logging for this
case.

Change-Id: Iffb1dd26bfc656e9ca8cf1f179b90e501f3da949
Signed-off-by: Ed Tanous <ed.tanous@intel.com>