[CI] Adds flake8 + flakeplus targets

tox.ini

@@ -1,5 +1,5 @@
 [tox]
-envlist = 2.7,pypy,3.4,3.5,pypy3
+envlist = 2.7,pypy,3.4,3.5,pypy3,flake8,flakeplus
 
 [testenv]
 deps=
@@ -27,9 +27,20 @@ basepython =
     3.5: python3.5
     pypy: pypy
     pypy3: pypy3
+    docs,flake8,flakeplus: python2.7
 
 [testenv:docs]
 deps = -r{toxinidir}/requirements/docs.txt
 commands =
     pip install -U -r{toxinidir}/requirements/dev.txt
     sphinx-build -W -b linkcheck -d {envtmpdir}/doctrees docs docs/_build/linkcheck
+
+[testenv:flake8]
+deps = -r{toxinidir}/requirements/pkgutils.txt
+commands =
+    flake8 {toxinidir}/celery
+
+[testenv:flakeplus]
+deps = -r{toxinidir}/requirements/pkgutils.txt
+commands =
+    flakeplus --2.6 {toxinidir}/celery