tox: rename pep8 to linters

pep8 is legacy, we now use flake8 and the virtual environment also runs
mypy and openapi-spec-validator.

Rename the virtualenv from 'pep8' to 'linters'.

Use tox-linters instead of tox-pep8.

tox-pep8 skips test-setup.sh Ia140b331ae1502fcf1f685faa6dace117d77d35d

Done for tox-linters by Idc72c7d1a88fff8e738c896e2482b5cb1d844600

Depends-On: Idc72c7d1a88fff8e738c896e2482b5cb1d844600
Change-Id: I1fbd8335a2353f750f49b6a763eefc6f399a7143

.zuul.yaml

@@ -203,7 +203,7 @@
       jobs:
         - zuul-build-image
         - zuul-tox-docs
-        - tox-pep8
+        - tox-linters
         - tox-py35:
             irrelevant-files:
               - zuul/cmd/migrate.py
@@ -259,7 +259,7 @@
       jobs:
         - zuul-upload-image
         - zuul-tox-docs
-        - tox-pep8
+        - tox-linters
         - tox-py35:
             irrelevant-files:
               - zuul/cmd/migrate.py

tox.ini

@@ -1,7 +1,7 @@
 [tox]
 minversion = 3.2
 skipsdist = True
-envlist = pep8,py3{-docker}
+envlist = linters,py3{-docker}
 ignore_basepython_conflict = True
 # TODO(stephenfin): It would be good to set 'requires = tox-docker', but doing
 # so borks the tools/pip.sh wrapper we're using here and probably isn't what
@@ -45,7 +45,7 @@ install_command = pip install {opts} {packages}
 deps = bindep
 commands = bindep test
 
-[testenv:pep8]
+[testenv:linters]
 install_command = pip install {opts} {packages}
 # --ignore-missing-imports tells mypy to not try to follow imported modules
 # out of the current tree. As you might expect, we don't want to run static