added a mock for Compute::RackspaceV2 delete_image; Compute::RackspaceV2 has not implemented mocking support however

lib/fog/rackspace/compute_v2.rb

@@ -54,9 +54,15 @@ module Fog
       request :delete_attachment
 
       class Mock
+        
+        def initialize(options)
+          # prevents service initialization errors. This method should be implemented
+        end
+        
         def request(params)
           Fog::Mock.not_implemented
         end
+        
       end
 
       class Real

lib/fog/rackspace/requests/compute_v2/delete_image.rb

@@ -17,6 +17,15 @@ module Fog
         end
 
       end
+      
+      class Mock
+        def delete_image(image_id)
+          response = Excon::Response.new
+          response.status = 202
+          response.body = "" 
+        end 
+        
+      end
     end
   end
 end