created separate 'image_name' field to allow user to specify desired VM through TOSCA;
if 'default' used for 'image_name', will use slice's default image

Change-Id: I2cc286c91915fdb8ca24c949ad25255841b8c15f
(cherry picked from commit 22afba8579f13386982d8043109c99b53c0c01af)
diff --git a/xos/tosca/resources/vmmetenant.py b/xos/tosca/resources/vmmetenant.py
index 848d2c8..2a6e6d4 100644
--- a/xos/tosca/resources/vmmetenant.py
+++ b/xos/tosca/resources/vmmetenant.py
@@ -4,8 +4,8 @@
 class XOSVMMETenant(XOSResource):
     provides = "tosca.nodes.VMMETenant"
     xos_model = VMMETenant
-    copyin_props = ["tenant_message"]  #should this be a list or a tuple (as in exampleservice) ? 
-    name_field = None  #should this be "service_specific id" (as in exampleservice) ? 
+    copyin_props = ["tenant_message", "image_name"]  
+    name_field = None  
 
     def get_xos_args(self, throw_exception=True):
         args = super(XOSVMMETenant, self).get_xos_args()