[ussuri][goal] drop python 2.7 support

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: I0b8a896ce64a4b31c11444a2af45ae503ad089f1

setup.cfg

@@ -6,6 +6,7 @@ description-file =
 author = Adrian Turjak
 author-email = adriant@catalyst.net.nz
 home-page = https://github.com/openstack/python-adjutantclient
+python-requires = >=3.6
 classifier =
     Environment :: OpenStack
     Intended Audience :: Information Technology
@@ -13,9 +14,11 @@ classifier =
     License :: OSI Approved :: Apache Software License
     Operating System :: POSIX :: Linux
     Programming Language :: Python
-    Programming Language :: Python :: 2
-    Programming Language :: Python :: 2.7
-    Programming Language :: Python :: 2.6
+    Programming Language :: Python :: Implementation :: CPython
+    Programming Language :: Python :: 3 :: Only
+    Programming Language :: Python :: 3
+    Programming Language :: Python :: 3.6
+    Programming Language :: Python :: 3.7
 
 [files]
 packages =
@@ -59,6 +62,3 @@ openstack.admin_logic.v1 =
 [global]
 setup-hooks =
     pbr.hooks.setup_hook
-
-[wheel]
-universal = 1

tox.ini

@@ -1,9 +1,11 @@
 [tox]
-minversion = 1.6
-envlist = py35,py27
+minversion = 3.1
+envlist = py35,py37
 skipsdist = True
+ignore_basepython_conflict = True
 
 [testenv]
+basepython = python3
 usedevelop = True
 install_command = pip install -c{env:UPPER_CONSTRAINTS_FILE:https://git.openstack.org/cgit/openstack/requirements/plain/upper-constraints.txt} {opts} {packages}
 setenv = VIRTUAL_ENV={envdir}
@@ -20,11 +22,9 @@ whitelist_externals = find
 sitepackages = True
 
 [testenv:pep8]
-basepython = python3
 commands = flake8
 
 [testenv:cover]
-basepython = python3
 commands =
   coverage erase
   find . -type f -name "*.pyc" -delete
@@ -32,11 +32,9 @@ commands =
   coverage report
 
 [testenv:venv]
-basepython = python3
 commands = {posargs}
 
 [testenv:docs]
-basepython = python3
 commands = python setup.py build_sphinx
 
 [flake8]
@@ -45,7 +43,6 @@ exclude=.venv,.git,.tox,dist,*lib/python*,*egg,build,doc/source/conf.py,releasen
 
 
 [testenv:bindep]
-basepython = python3
 # Do not install any requirements. We want this to be fast and work even if
 # system dependencies are missing, since it's used to tell you what system
 # dependencies are missing! This also means that bindep must be installed