Use img['checksum'] as origin disk param.

Use the img['checksum'], instead of img['backend_id'] as the origin disk
paramater, as neede by the new archipelago code (and drop support for the old
one).

snf-cyclades-app/synnefo/api/servers.py

@@ -295,6 +295,7 @@ def create_server(request):
         properties = img.get('properties', {})
         image['backend_id'] = img['location']
         image['format'] = img['disk_format']
+        image['checksum'] = img['checksum']
         image['metadata'] = dict((key.upper(), val) \
                                  for key, val in properties.items())
 

snf-cyclades-app/synnefo/logic/backend.py

@@ -312,7 +312,7 @@ def create_instance(vm, public_nic, flavor, image, password, personality):
         kw['disks'][0]['provider'] = provider
 
         if provider == 'vlmc':
-            kw['disks'][0]['origin'] = image['backend_id']
+            kw['disks'][0]['origin'] = image['checksum']
 
     kw['nics'] = [public_nic]
     if settings.GANETI_USE_HOTPLUG:
@@ -339,7 +339,7 @@ def create_instance(vm, public_nic, flavor, image, password, personality):
     if personality:
         kw['osparams']['img_personality'] = json.dumps(personality)
 
-    if provider != None and provider == 'vlmc':
+    if provider == 'vlmc':
         kw['osparams']['img_id'] = 'null'
 
     kw['osparams']['img_properties'] = json.dumps(image['metadata'])