Add backupninja group explicitly

This patch ensures that "backupninja" group is created prior to creating
"backupninja" user

Change-Id: I37b2d6632e4e0e4b05feeaefc8f3f5028c048cbd
Related-PROD: PROD-23546
diff --git a/backupninja/server.sls b/backupninja/server.sls
index 58bf986..aad237a 100644
--- a/backupninja/server.sls
+++ b/backupninja/server.sls
@@ -10,6 +10,15 @@
   - name: backupninja
   - system: true
   - home: {{ server.home_dir }}
+  - groups:
+    - backupninja
+
+backupninja_group:
+  group.present:
+  - name: backupninja
+  - system: true
+  - require_in:
+    - user: backupninja_user
 
 {{ server.home_dir }}:
   file.directory: