Create a wsgi factory method for Debug filter.

This can be enabled by putting the following in the *-paste.ini
file:
[filter:debug]
paste.filter_factory = heat.common.wsgi:filter_factory
heat.filter_factory = heat.common.wsgi:debug_filter

and adding 'debug' to the pipeline.

This assisted with bug #1133792

Change-Id: I4c2d3194ac9673d095b4115d4b6f385fd2f4fa4e
Merge "Create a wsgi factory method for Debug filter."