schema-version added in VNFD, NSD, VLR, VNFR and NSR

Change-Id: I718533b5fd5dac26d07f2093f42485e56de6adc9
Signed-off-by: garciadeblas <gerardo.garciadeblas@telefonica.com>
diff --git a/models/yang/vnfd.yang b/models/yang/vnfd.yang
index d1c9df6..4816166 100644
--- a/models/yang/vnfd.yang
+++ b/models/yang/vnfd.yang
@@ -43,6 +43,12 @@
     description
       "Virtual Network Function Descriptor (VNFD).";
 
+    leaf schema-version {
+      description "Schema version for the VNFD. If unspecified, it assumes v3.0";
+      type string;
+      default "v3.0";
+    }
+
     list vnfd {
       key "id";