[spec] fix the "undefined method `running_disabled_spec='" if use TAP

This patch should fix the following error if use TAP output format.
	ERROR: NoMethodError - undefined method `running_disabled_spec=' for Bacon:Class

My jenkins CI uses TAP format <3

test/helpers/bacon.rb

@@ -112,5 +112,9 @@ module Bacon
     end
   end
 
+  module TapOutput
+    attr_accessor :running_disabled_spec
+  end
+
   Outputs['pretty_spec_dox'] = PrettySpecDoxOutput
 end