Unit tests improvements

- From now on, black must pass. Jenkins will give a -1 if it doesn't
- Ignore E203 because it is not pep8 compliant, and conflicts with black
    https://github.com/psf/black/issues/315#issuecomment-395457972
- Black fixes and minor fix in unit test
- Fix devops-stages/stage-test.sh: jenkins was not giving a -1 when tox
was failing

Change-Id: Ic7318dcb6d4006a271607cd064a1f36d0936b7b9
Signed-off-by: David Garcia <david.garcia@canonical.com>
diff --git a/n2vc/loggable.py b/n2vc/loggable.py
index b3b98da..d588a1d 100644
--- a/n2vc/loggable.py
+++ b/n2vc/loggable.py
@@ -115,7 +115,7 @@
         if not include_path:
             i = filename.rfind("/")
             if i > 0:
-                filename = filename[i + 1:]
+                filename = filename[i + 1 :]
 
         # datetime
         dt = datetime.datetime.now().strftime("%Y-%m-%d %H:%M:%S.%f")