Pass debug mode to eventlet.wsgi.server

Previously if any exceptions accidentally made their way to
eventlet.wsgi.server's response handler it would print their traceback.
We only want to show users tracebacks in debug mode. In production we
want them suppressed.

Fixes bug #1222008
Change-Id: Ieb11f75ebffc67bd584432cfd8eeaac010fce7ca
Merge "Pass debug mode to eventlet.wsgi.server"