Drop support for python 2

This is modelled on the similar change in nova [1] but is
simpler because Placement was already using python3 for
"integration" style tests.

The 'train' python3 template is replaced with corresponding 'ussuri'.

The python template is removed (it is 2.7) and the pep8 job that was
included in that template is now listed in check and gate jobs.

.zuul.yaml is updated to not do a generic 'funtional' test,
instead versioned tests only.

setup.cfg removes indications of support for python 2.

A reno is added.

tox.ini is changed to make the functional environment a
base environment for specific functional jobs.

[1] Ie1a0cbd82a617dbcc15729647218ac3e9cd0e5a9

Change-Id: Ifce3b0c0ff11553f32b2d02df07fde81efc34100

.zuul.yaml

@@ -10,14 +10,13 @@
       - publish-openstack-docs-pti
       - openstack-cover-jobs
       - openstack-lower-constraints-jobs
-      - openstack-python-jobs
-      - openstack-python3-train-jobs
+      - openstack-python3-ussuri-jobs
       - release-notes-jobs-python3
     check:
       jobs:
-        - openstack-tox-functional
         - openstack-tox-functional-py36
         - openstack-tox-functional-py37
+        - openstack-tox-pep8
         - placement-nova-tox-functional-py37
         - placement-nested-perfload:
             voting: false
@@ -46,9 +45,9 @@
             irrelevant-files: *gate-irrelevant-files
     gate:
       jobs:
-        - openstack-tox-functional
         - openstack-tox-functional-py36
         - openstack-tox-functional-py37
+        - openstack-tox-pep8
         - placement-nova-tox-functional-py37
         - tempest-integrated-placement:
             irrelevant-files: *gate-irrelevant-files

releasenotes/notes/drop-python-2-aabea7dcdeca7ebf.yaml

@@ -0,0 +1,5 @@
+---
+upgrade:
+  - |
+    Python 2.7 support has been dropped. The minimum version of Python now
+    supported by placement is Python 3.6.

setup.cfg

@@ -19,8 +19,6 @@ 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 :: 3.6
     Programming Language :: Python :: 3.7

tox.ini

@@ -1,6 +1,6 @@
 [tox]
 minversion = 3.1.1
-envlist = py27,py37,functional,functional-py37,pep8
+envlist = py37,functional-py37,pep8
 skipsdist = True
 # Automatic envs (pyXX) will use the python version appropriate to that
 # env and ignore basepython inherited from [testenv]. That's what we
@@ -34,12 +34,8 @@ passenv =
 # there is also secret magic in subunit-trace which lets you run in a fail only
 # mode. To do this define the TRACE_FAILONLY environmental variable.
 
-# The functional environment is both the base env for functional tests and
-# also the python 2.7 version of functional tests. This is a historical
-# artifact.
+# The functional environment is the base env for functional tests.
 [testenv:functional]
-basepython = python2.7
-envdir = {toxworkdir}/py27
 commands =
   stestr --test-path=./placement/tests/functional run {posargs}