pythonlib/riotctrl_ctrl: add black testenv in tox

Add Flake8 configuration compatible with black

dist/pythonlibs/riotctrl_ctrl/setup.cfg

@@ -0,0 +1,5 @@
+# Use black compatible configuration for flake8
+# https://black.readthedocs.io/en/stable/guides/using_black_with_other_tools.html#flake8
+[flake8]
+max-line-length = 88
+extend-ignore = E203

dist/pythonlibs/riotctrl_ctrl/tox.ini

@@ -1,11 +1,12 @@
 [tox]
-envlist = test,flake8
+envlist = test,flake8,black
 skipsdist = True
 
 [testenv]
 commands =
     test:       {[testenv:test]commands}
     flake8:     {[testenv:flake8]commands}
+    black:      {[testenv:black]commands}
 
 [testenv:test]
 deps =
@@ -18,3 +19,11 @@ commands =
 deps = flake8
 commands =
     flake8 .
+
+[testenv:black]
+allowlist_externals =
+    /usr/bin/bash
+    /bin/bash
+deps = black
+commands =
+    bash -c "black --check --diff --color tests/ *.py"