prevent @@subclasses from being emptied

This can happen due to Chef's stupid approach to loading library files,
which uses Kernel#load rather than #require.  Consequently a library
can get loaded twice: once by Chef::RunContext#load_libraries and once
by another library file which depends on it.

This is also the cause of the TYPE constants being redefined.

libraries/pacemaker/cib_object.rb

@@ -4,7 +4,7 @@ module Pacemaker
   class CIBObject
     attr_accessor :name, :definition
 
-    @@subclasses = { }
+    @@subclasses = { } unless class_variable_defined?(:@@subclasses)
 
     class << self
       attr_reader :object_type