Cleanup Python 2.7 support

OpenStack is dropping the py2.7 support in ussuri cycle.

Make a few cleanups:
- Remove python 2.7 stanza from setup.py
- Add requires on python >= 3.6 to setup.cfg so that pypi and pip
  know about the requirement
- Remove section from setup.cfg: Wheel is not needed for python
  3 only repo
- Update requirements

Change-Id: Ibca03f9ebaeaca595e027be9cb5900c368c8de6d

doc/requirements.txt

@@ -4,7 +4,7 @@
 openstackdocstheme>=1.31.2 # Apache-2.0
 reno>=2.5.0 # Apache-2.0
 doc8>=0.6.0 # Apache-2.0
-sphinx!=1.6.6,!=1.6.7,!=2.1.0,>=1.6.2;python_version>='3.4'  # BSD
+sphinx!=1.6.6,!=1.6.7,!=2.1.0,>=1.6.2 # BSD
 mock>=2.0.0 # BSD
 os-api-ref>=1.4.0 # Apache-2.0
 ddt>=1.0.1 # MIT

requirements.txt

@@ -9,7 +9,6 @@ alembic>=0.8.10 # MIT
 Babel!=2.4.0,>=2.3.4 # BSD
 eventlet!=0.18.3,!=0.20.1,>=0.18.2 # MIT
 greenlet>=0.4.10 # MIT
-ipaddress>=1.0.17;python_version<'3.3' # PSF
 lxml!=3.7.0,>=3.4.1 # BSD
 netaddr>=0.7.18 # BSD
 oslo.config>=5.2.0 # Apache-2.0

setup.cfg

@@ -6,6 +6,7 @@ description-file =
 author = OpenStack
 author-email = openstack-discuss@lists.openstack.org
 home-page = https://docs.openstack.org/manila/latest/
+python-requires = >=3.6
 classifier =
     Environment :: OpenStack
     Intended Audience :: Information Technology
@@ -104,6 +105,3 @@ input_file = manila/locale/manila.pot
 keywords = _ gettext ngettext l_ lazy_gettext
 mapping_file = babel.cfg
 output_file = manila/locale/manila.pot
-
-[wheel]
-universal = 1

setup.py

@@ -16,14 +16,6 @@
 # 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>=2.0.0'],
     pbr=True)