Drop python 2.7 support and testing

Change-Id: I3ff7a714d5fd61edd72e00c7a454c81724844f99
Closes-bug: #1853372

.zuul.yaml

@@ -28,6 +28,7 @@
       devstack_localrc:
         CINDER_ISCSI_HELPER: lioadm
         TEMPEST_PLUGINS: /opt/stack/cinder-tempest-plugin
+        USE_PYTHON3: true
       devstack_plugins:
         barbican: https://opendev.org/openstack/barbican
       devstack_services:

setup.cfg

@@ -13,10 +13,9 @@ 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 :: 3
-    Programming Language :: Python :: 3.5
+    Programming Language :: Python :: 3.6
+    Programming Language :: Python :: 3.7
 
 [files]
 packages =

test-requirements.txt

@@ -6,8 +6,7 @@ hacking!=0.13.0,<0.14,>=0.12.0 # Apache-2.0
 
 coverage!=4.4,>=4.0 # Apache-2.0
 python-subunit>=1.0.0 # Apache-2.0/BSD
-sphinx!=1.6.6,!=1.6.7,>=1.6.2,<2.0.0;python_version=='2.7'  # BSD
-sphinx!=1.6.6,!=1.6.7,>=1.6.2;python_version>='3.4'  # BSD
+sphinx!=1.6.6,!=1.6.7,>=1.6.2 # BSD
 oslotest>=3.2.0 # Apache-2.0
 testrepository>=0.0.18 # Apache-2.0/BSD
 testtools>=2.2.0 # MIT

tox.ini

@@ -1,9 +1,13 @@
 [tox]
-minversion = 2.0
+minversion = 3.1.0
 envlist = pep8
 skipsdist = True
+# this allows tox to infer the base python from the environment name
+# and override any basepython configured in this file
+ignore_basepython_conflict=true
 
 [testenv]
+basepython = python3
 usedevelop = True
 install_command = pip install {opts} {packages}
 setenv =
@@ -14,11 +18,9 @@ deps = -c{env:UPPER_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/
 commands = python setup.py test --slowest --testr-args='{posargs}'
 
 [testenv:pep8]
-basepython = python3
 commands = flake8 {posargs}
 
 [testenv:venv]
-basepython = python3
 commands = {posargs}
 
 [flake8]