Revert "Cleanup py27 support"

This partially reverts commit 60c1454e95.

It only reverts the py27 changes, not the docs change since that is
not relevant for py27.

Because swift still has some remaining known issue with Py3,
we still need to keep py2 compatibility during Ussuri cycle.

Change-Id: I3d6e1363a7f001618b594ded8bdaefc3164544f6

setup.cfg

@@ -6,7 +6,6 @@ description-file =
 author = OpenStack
 author-email = openstack-discuss@lists.openstack.org
 home-page = https://docs.openstack.org/storlets/latest/
-python-requires = >=3.6
 classifier =
     Environment :: OpenStack
     Intended Audience :: Information Technology
@@ -14,8 +13,6 @@ classifier =
     License :: OSI Approved :: Apache Software License
     Operating System :: POSIX :: Linux
     Programming Language :: Python
-    Programming Language :: Python :: Implementation :: CPython
-    Programming Language :: Python :: 3 :: Only
     Programming Language :: Python :: 3
     Programming Language :: Python :: 3.6
     Programming Language :: Python :: 3.7

setup.py

@@ -1,3 +1,4 @@
+#!/usr/bin/env python
 # Copyright (c) 2013 Hewlett-Packard Development Company, L.P.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
@@ -13,8 +14,17 @@
 # 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>=1.9', 'setuptools>=17.1'],
+    setup_requires=['pbr'],
     pbr=True)