added 'image_name' property to vPGWC Tenant model
you can now choose which VM you want for a given instance
in tosca using the 'image_name' property

Change-Id: I2f889caf6640d96c18f2cb006d3270cd8cb4555a
diff --git a/xos/tosca/resources/VPGWCTenant.py b/xos/tosca/resources/VPGWCTenant.py
index afd6966..434972a 100644
--- a/xos/tosca/resources/VPGWCTenant.py
+++ b/xos/tosca/resources/VPGWCTenant.py
@@ -4,7 +4,7 @@
 class XOSVPGWCTenant(XOSResource):
     provides = "tosca.nodes.VPGWCTenant"
     xos_model = VPGWCTenant
-    copyin_props = ["s5s8_pgw_tag", "display_message"]
+    copyin_props = ["s5s8_pgw_tag", "display_message", "image_name"]
     name_field = None
 
     def get_xos_args(self, throw_exception=True):