tox: Ignore .venv files for flake8

Commonly used for testing virtual environments (at least by me).

Change-Id: I3b711bd3464a2ca2a8dced37d9d6ec328b8bf827
Signed-off-by: Stephen Finucane <stephenfin@redhat.com>

tox.ini

@@ -59,7 +59,7 @@ commands = sphinx-build -a -E -W -d releasenotes/build/doctrees -b html releasen
 
 [flake8]
 show-source = True
-exclude = .git,.tox,dist,doc,*lib/python*,*egg,build,tools
+exclude = .venv,.git,.tox,dist,doc,*lib/python*,*egg,build,tools
 # If 'ignore' is not set there are default errors and warnings that are set
 # Doc: http://flake8.readthedocs.org/en/latest/config.html#default
 ignore = W504