Run uWSGI as barbican user

Parameterizes the user that uWSGI is running as, and sets it to the barbican user by default.  In order for this to work though, you need to make sure that the permissions on python_dateutil don't interfere.

[barbican@berkshelf python2.6]$ find site-packages/python_dateutil-2.2-py2.6.egg-info/ -perm 600
site-packages/python_dateutil-2.2-py2.6.egg-info/dependency_links.txt
site-packages/python_dateutil-2.2-py2.6.egg-info/top_level.txt
site-packages/python_dateutil-2.2-py2.6.egg-info/PKG-INFO
site-packages/python_dateutil-2.2-py2.6.egg-info/not-zip-safe
site-packages/python_dateutil-2.2-py2.6.egg-info/SOURCES.txt
site-packages/python_dateutil-2.2-py2.6.egg-info/requires.txt