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/synchronizer/steps/sync_vsgw.py b/xos/synchronizer/steps/sync_vsgw.py
index ddc06e9..375c3a1 100644
--- a/xos/synchronizer/steps/sync_vsgw.py
+++ b/xos/synchronizer/steps/sync_vsgw.py
@@ -36,5 +36,6 @@
     def get_extra_attributes(self, o):
         fields = {}
         fields['tenant_message'] = o.tenant_message
+        fields['image_name'] = o.image_name
         return fields