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/k8s_helm_base_conn.py b/n2vc/k8s_helm_base_conn.py
index ad59e8b..4a43ee2 100644
--- a/n2vc/k8s_helm_base_conn.py
+++ b/n2vc/k8s_helm_base_conn.py
@@ -1471,11 +1471,11 @@
         # check embeded chart (file or dir)
         if chart_name.startswith("/"):
             # extract file or directory name
-            chart_name = chart_name[chart_name.rfind("/") + 1:]
+            chart_name = chart_name[chart_name.rfind("/") + 1 :]
         # check URL
         elif "://" in chart_name:
             # extract last portion of URL
-            chart_name = chart_name[chart_name.rfind("/") + 1:]
+            chart_name = chart_name[chart_name.rfind("/") + 1 :]
 
         name = ""
         for c in chart_name: