Minor cleanup to test publishing

Remove now obsolete python 2.7.x support from setup.py,
update pbr version and make dependency explicit via requirements.txt

This change was pushed to test that the dependent change fixes
publishing content to https://service-types.openstack.org/ . So,
please merge once dependency is in and then we can check that publishing
to server works correctly.

Depends-On: https://review.opendev.org/709060
Change-Id: Iac2be67dbef5510679f5cda658b591e52d537051

requirements.txt

@@ -1,3 +1,4 @@
+pbr!=2.1.0,>=2.0.0 # Apache-2.0
 hacking
 jsonschema
 requests

setup.py

@@ -13,17 +13,8 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-# THIS FILE IS MANAGED BY THE GLOBAL REQUIREMENTS REPO - DO NOT EDIT
 import setuptools
 
-# In python < 2.7.4, a lazy loading of package `pbr` will break
-# setuptools if some other modules registered functions in `atexit`.
-# solution from: http://bugs.python.org/issue15881#msg170215
-try:
-    import multiprocessing  # noqa
-except ImportError:
-    pass
-
 setuptools.setup(
-    setup_requires=['pbr>=1.8'],
+    setup_requires=['pbr>=2.0.0'],
     pbr=True)