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
- Update requirements, no need for python_version anymore

Change-Id: I547968d14abbdb8d134d7a94a545ea38342ec6a1
diff --git a/setup.cfg b/setup.cfg
index d4167e3..6986526 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -6,6 +6,7 @@
 author = OpenStack
 author-email = openstack-discuss@lists.openstack.org
 home-page = https://www.openstack.org/
+python-requires = >=3.6
 classifier =
     Environment :: OpenStack
     Intended Audience :: Information Technology
@@ -13,6 +14,8 @@
     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
@@ -25,15 +28,6 @@
 tempest.test_plugins =
     telemetry_tests = telemetry_tempest_plugin.plugin:TelemetryTempestPlugin
 
-[build_sphinx]
-all-files = 1
-warning-is-error = 1
-source-dir = doc/source
-build-dir = doc/build
-
-[upload_sphinx]
-upload-dir = doc/build/html
-
 [compile_catalog]
 directory = telemetry_tempest_plugin/locale
 domain = telemetry_tempest_plugin