chore: Combine pep8 with whitespace linter

This patch set combines whitespace linter and pep8 together
(as both do code linting) into the same job by dropping the
.zuul.yaml whitespace-linter job and rolling it up into the
same pep8 tox.ini check, just like Deckhand [0].

[0] 0462b7b929/tox.ini (L106)

Change-Id: I31ed60adfd431157ffc96a0f4d5d77d54af37352

tox.ini

@@ -13,6 +13,7 @@ setenv=
 usedevelop = True
 install_command = pip install {opts} {packages}
 whitelist_externals =
+    bash
     find
     rm
 commands =
@@ -69,6 +70,8 @@ deps =
     .[bandit]
     {[testenv]deps}
 commands =
+    # Whitespace linter (for chart files)
+    bash {toxinidir}/tools/whitespace-linter.sh
     yapf -dr {toxinidir}/armada {toxinidir}/setup.py
     flake8 {posargs}
     # Run security linter as part of the pep8 gate instead of a separate zuul job.