Add wsgi_intercept to global_requirements

The Trove unit tests require the wsgi_intercept>0.6.1 python package
which doesn't exist in in the global requirements today.
Adding this package requirement to the global requirements.
The library was tested on: Python 2.6.9, Python 2.7.3, and
Python 3.2.3

Change-Id: I62c139c3754f5aefe718ad12e1d61bc054708f4c
Merge "Add wsgi_intercept to global_requirements"