Add default_kernel_name class level variable

IPython/html/static/notebook/js/notebook.js

@@ -59,6 +59,9 define([
         this.keyboard_manager = options.keyboard_manager;
         this.save_widget = options.save_widget;
         this.tooltip = new tooltip.Tooltip(this.events);
+        // default_kernel_name is a temporary measure while we implement proper
+        // kernel selection and delayed start. Do not rely on it.
+        this.default_kernel_name = 'python';
         // TODO: This code smells (and the other `= this` line a couple lines down)
         // We need a better way to deal with circular instance references.
         this.keyboard_manager.notebook = this;
@@ -1498,7 +1501,7 define([
             // For now, create all sessions with the 'python' kernel, which is the
             // default. Later, the user will be able to select kernels. This is
             // overridden if KernelManager.kernel_cmd is specified for the server.
-            kernel_name: 'python',
+            kernel_name: this.default_kernel_name,
             notebook: this});
 
         this.session.start($.proxy(this._session_started, this));