Stop testing python2.7

Train was the last release supporting python2. Let's rip the bandaid
off.

Change-Id: I5ba95cd95b60002ba3a5fc261b74db7c98581fd4

.zuul.yaml

@@ -3,7 +3,6 @@
       - openstack-python-jobs
       - openstack-python35-jobs
       - openstack-python3-ussuri-jobs
-      - tempest-plugin-jobs
       - check-requirements
     gate:
       queue: ec2-api

setup.cfg

@@ -13,8 +13,6 @@ 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 :: 3.5
     Programming Language :: Python :: 3.6

tox.ini

@@ -1,10 +1,11 @@
 [tox]
 minversion = 2.0
-envlist = py27,py37,pep8
+envlist = py37,pep8
 skipsdist = True
 
 [testenv]
 usedevelop = True
+basepython = python3
 # tox is silly... these need to be separated by a newline....
 whitelist_externals = bash
                       find
@@ -26,15 +27,12 @@ commands =
   rm -f .testrepository/times.dbm
 
 [testenv:pep8]
-basepython = python3
 commands = flake8 {posargs}
 
 [testenv:venv]
-basepython = python3
 commands = {posargs}
 
 [testenv:debug]
-basepython = python3
 commands = oslo_debug_helper {posargs}
 
 [flake8]