[ussuri][goal] Updates for python 2.7 drop

OpenStack is dropping the py2.7 support in ussuri cycle except
swift and sorlets which is exception approved in this goal.

Somehow this repo is left to remove the support of py2.7.

Ussuri Communtiy-wide goal:
https://governance.openstack.org/tc/goals/selected/ussuri/drop-py27.html

Change-Id: Id30a4bbee9a437d8e73dc71f0b65304dc5e64e23

setup.cfg

@@ -7,6 +7,7 @@ author = OpenStack
 author-email = openstack-discuss@lists.openstack.org
 license = Apache License (2.0)
 home-page = https://opendev.org/openstack/tripleo-image-elements
+python-requires = >=3.6
 classifier =
     Environment :: OpenStack
     Development Status :: 3 - Alpha
@@ -15,8 +16,8 @@ classifier =
     Programming Language :: Other
     Environment :: Console
     Programming Language :: Python
-    Programming Language :: Python :: 2
-    Programming Language :: Python :: 2.7
+    Programming Language :: Python :: Implementation :: CPython
+    Programming Language :: Python :: 3 :: Only
     Programming Language :: Python :: 3
     Programming Language :: Python :: 3.6
     Programming Language :: Python :: 3.7
@@ -24,11 +25,3 @@ classifier =
 [files]
 data_files =
     share/tripleo-image-elements = elements/*
-
-[wheel]
-universal = 1
-
-[build_sphinx]
-all_files = 1
-build-dir = doc/build
-source-dir = doc/source

test-requirements.txt

@@ -2,7 +2,6 @@ hacking>=1.1.0,<1.2.0 # Apache-2.0
 openstackdocstheme>=1.11.0  # Apache-2.0
 
 oslotest
-sphinx>=1.8.0,<2.0.0;python_version=='2.7' # BSD
-sphinx>=1.8.0,!=2.1.0;python_version>='3.4' # BSD
+sphinx>=1.8.0,!=2.1.0 # BSD
 testrepository>=0.0.18
 reno>=1.8.0 # Apache-2.0