Update hacking for Python3

The repo is Python 3 now, so update hacking to version 3.0 which
supports Python 3.

Fix problems found.

Update local hacking checks for new flake8.

Remove hacking and friends from lower-constraints, they are not needed
to be installed at run-time.

Change-Id: Ia6af344ec8441dc98a0820176373dcff3a8c80d5

tox.ini

@@ -75,7 +75,8 @@ commands =
 [flake8]
 filename = *.py,app.wsgi
 show-source=True
-ignore= H105,E123,E226,N320,H202
+# W504 line break after binary operator
+ignore= H105,E123,E226,N320,H202,W504
 builtins= _
 enable-extensions = H106,H203,H904
 exclude=.venv,.git,.tox,dist,doc,*lib/python*,*egg,build,*sqlalchemy/alembic/versions/*,demo/,releasenotes
@@ -85,7 +86,26 @@ commands = python setup.py bdist_wheel
 
 [hacking]
 import_exceptions = watcher._i18n
-local-check-factory = watcher.hacking.checks.factory
+
+[flake8:local-plugins]
+extension =
+   N319 = checks:no_translate_debug_logs
+   N321 = checks:use_jsonutils
+   N322 = checks:check_assert_called_once_with
+   N325 = checks:check_python3_xrange
+   N326 = checks:check_no_basestring
+   N327 = checks:check_python3_no_iteritems
+   N328 = checks:check_asserttrue
+   N329 = checks:check_assertfalse
+   N330 = checks:check_assertempty
+   N331 = checks:check_assertisinstance
+   N332 = checks:check_assertequal_for_httpcode
+   N333 = checks:check_log_warn_deprecated
+   N340 = checks:check_oslo_i18n_wrapper
+   N341 = checks:check_builtins_gettext
+   N342 = checks:no_redundant_import_alias
+paths = ./watcher/hacking
+
 
 [doc8]
 extension=.rst