pbr is removing support for wsgi_script due to changes in setuptools.
Use the wsgi script module python code instead.
Note that this change only touches CentOS code. Ubuntu and Debian will
be updated later when we bump the release used in our testing.
Change-Id: Ib724af2a20677937d7e9e9b417731296b64c7279
Signed-off-by: Takashi Kajinami <kajinamit@oss.nttdata.com>