Stop supporting python2

OpenStack Infra is running Zuul v3 on Python3. We're adding things, like
the websockets streaming, that are python3 only - and testing them turns
out to be extra hard even with skipTest because of the syntax changes.
There are no legacy Zuul v3 installations to worry about, and the
Software Factory team has verified that Python3 on CentOS 7 is not a
problem. It's time to pull the plug.

Remove python2 jobs from running in v3. Make the tox defaults python3
for all testenvs and update setup.cfg to indicate that Zuul v3 supports
python3 and not python2.

Also fixed a python3 bug in zuul command line client that shows up
when running zuul --help under python3.

Change-Id: Icaccab9f6edcdba0b87ec0b5f0411d3dc8030b42

.zuul.yaml

@@ -5,6 +5,5 @@
         - tox-docs
         - tox-cover
         - tox-linters
-        - tox-py27
         - tox-py35
         - tox-tarball

setup.cfg

@@ -12,9 +12,8 @@ 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 :: 3
+    Programming Language :: Python :: 3.5
 
 [pbr]
 warnerrors = True

tox.ini

@@ -1,9 +1,10 @@
 [tox]
 minversion = 1.6
 skipsdist = True
-envlist = pep8, py27
+envlist = pep8,py35
 
 [testenv]
+basepython = python3
 # Set STATSD env variables so that statsd code paths are tested.
 setenv = STATSD_HOST=127.0.0.1
          STATSD_PORT=8125
@@ -27,7 +28,6 @@ commands = bindep test
 
 [testenv:pep8]
 # streamer is python3 only, so we need to run flake8 in python3
-basepython = python3
 commands = flake8 {posargs}
 
 [testenv:cover]

zuul/cmd/client.py

@@ -95,10 +95,11 @@ class Client(zuul.cmd.ZuulApp):
             'running-jobs',
             help='show the running jobs'
         )
+        running_jobs_columns = list(self._show_running_jobs_columns().keys())
         show_running_jobs.add_argument(
             '--columns',
             help="comma separated list of columns to display (or 'ALL')",
-            choices=self._show_running_jobs_columns().keys().append('ALL'),
+            choices=running_jobs_columns.append('ALL'),
             default='name, worker.name, start_time, result'
         )