Cleanup py27 support

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 obsolete sections from setup.cfg:
  * Wheel is not needed for python 3 only repo
  * Some other sections are obsolete
- Update classifiers

Change-Id: I048ae7e3f916792f0a152db98487ae57bde9fd36

setup.cfg

@@ -7,6 +7,7 @@ license = Apache License, Version 2.0
 author = OpenStack
 author-email = openstack-discuss@lists.openstack.org
 home-page = https://docs.openstack.org/python-pankoclient/latest/
+python-requires = >=3.6
 classifier =
     Development Status :: 5 - Production/Stable
     Environment :: Console
@@ -16,6 +17,8 @@ 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
@@ -51,14 +54,6 @@ openstack.event.v2 =
     event trait list = pankoclient.v2.events_cli:EventTraitList
     event trait description = pankoclient.v2.events_cli:EventTraitDescription
 
-[build_sphinx]
-source-dir = doc/source
-build-dir = doc/build
-all_files = 1
-
-[upload_sphinx]
-upload-dir = doc/build/html
-
 [compile_catalog]
 directory = pankoclient/locale
 domain = pankoclient
@@ -72,11 +67,3 @@ input_file = pankoclient/locale/pankoclient.pot
 keywords = _ gettext ngettext l_ lazy_gettext
 mapping_file = babel.cfg
 output_file = pankoclient/locale/pankoclient.pot
-
-[build_releasenotes]
-all_files = 1
-build-dir = releasenotes/build
-source-dir = releasenotes/source
-
-[wheel]
-universal = 1

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'],
     pbr=True)