fixed typo in 'image' property, now 'VSGWTenant' instead of 'VMMETenant'

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

Change-Id: Idfcd29f871f31464d1c6e0717f000d0d5f603286
diff --git a/xos/tosca/resources/vsgwtenant.py b/xos/tosca/resources/vsgwtenant.py
index ecf6051..f53048a 100644
--- a/xos/tosca/resources/vsgwtenant.py
+++ b/xos/tosca/resources/vsgwtenant.py
@@ -5,7 +5,7 @@
     provides = "tosca.nodes.VSGWTenant"
     xos_model = VSGWTenant
     name_field = "service_specific_id"
-    copyin_props = ("tenant_message",)
+    copyin_props = ("tenant_message", "image_name")
 
     def get_xos_args(self, throw_exception=True):
         args = super(XOSVSGWTenant, self).get_xos_args()