setup.py: rename misleading (leftover?) variable name

It looks like the same block of code was used to read the requirements
file.  Let's rename it and avoid confusion.
Signed-off-by: NCleber Rosa <crosa@redhat.com>

setup.py

@@ -25,9 +25,9 @@ with open(os.path.join(BASE_PATH, 'VERSION'), 'r') as version_file:
 
 
 def get_long_description():
-    with open(os.path.join(BASE_PATH, 'README.rst'), 'r') as req:
-        req_contents = req.read()
-    return req_contents
+    with open(os.path.join(BASE_PATH, 'README.rst'), 'r') as readme:
+        readme_contents = readme.read()
+    return readme_contents
 
 
 INSTALL_REQUIREMENTS = ['stevedore>=0.14', 'setuptools']