Fix bug 1542 to allow juju to add Azure AKS

Storage classes in Azure might have no metadata annotations. This
change takes into account that situation.

Change-Id: I4f7151d2481b41fd8434e0d95ea5d1a156b68309
Signed-off-by: garciadeblas <gerardo.garciadeblas@telefonica.com>
diff --git a/n2vc/kubectl.py b/n2vc/kubectl.py
index bc8c392..d67f4db 100644
--- a/n2vc/kubectl.py
+++ b/n2vc/kubectl.py
@@ -96,7 +96,7 @@
             if not selected_sc:
                 # Select the first storage class in case there is no a default-class
                 selected_sc = sc.metadata.name
-            annotations = sc.metadata.annotations
+            annotations = sc.metadata.annotations or {}
             if any(
                 k in annotations and annotations[k] == v
                 for k, v in default_sc_annotations.items()