[pre-commit] enforce pre-commit checks in ci

This change moves all style checks to be run via pre-commit.

To enable this in existing ci and preserve the standard developer flow
the tox pep8 target is updated to run all checks via pre-commit.

developers can optionally install pre-commit and/or the pre-commit
commit hook to automatically or manually run the precommit hooks.

Change-Id: I6ee6ed853dbf60339e7bf3da66b2e5914c218f76

tox.ini

@@ -38,10 +38,14 @@ passenv =
   PYTHONOPTIMIZE
 
 [testenv:pep8]
+description =
+    Run style checks.
+skip_install = true
+deps =
+    pre-commit
 commands =
-    doc8 doc/source/ CONTRIBUTING.rst HACKING.rst README.rst
+    pre-commit run --all-files --show-diff-on-failure
-    flake8
+
-    #bandit -r watcher -x watcher/tests/* -n5 -ll -s B320
 
 [testenv:venv]
 setenv = PYTHONHASHSEED=0