added the ability to prohibit network access for code submissions executed using Docker

db/migrate/20150317115338_add_network_enabled_to_execution_environments.rb

@@ -0,0 +1,11 @@
+class AddNetworkEnabledToExecutionEnvironments < ActiveRecord::Migration
+  def change
+    add_column :execution_environments, :network_enabled, :boolean
+
+    reversible do |direction|
+      direction.up do
+        ExecutionEnvironment.update_all(network_enabled: true)
+      end
+    end
+  end
+end