eliminate "superclass mismatch for class Resource" error

Previously libraries/pacemaker/mixins/resource_meta.rb had:

  module Pacemaker
    class Resource
      module Meta
        ...

but libraries/pacemaker/resource.rb had:

  module Pacemaker
    class Resource < Pacemaker::CIBObject
      ...

This would work fine if libraries/pacemaker/resource.rb was loaded
before libraries/pacemaker/mixins/resource_meta.rb, because then
Pacemaker::Resource would have Pacemaker::CIBObject as its parent class,
and the mixin would simply add the Meta module within the existing
Pacemaker::Resource class.  However, due to Chef's somewhat erratic
method of loading libraries, sometimes it could happen the other way
around, in which case Pacemaker::Resource would be initially defined by
the mixin with no parent class, and then when resource.rb was loaded, it
would attempt to redefine Resource to have a parent class, triggering
the error.

libraries/pacemaker/mixins/resource_meta.rb

@@ -2,7 +2,8 @@
 # (priority, target-role, is-managed)
 
 module Pacemaker
-  class Resource
+  module Mixins
+    module Resource
       module Meta
         def self.included(base)
           base.extend ClassMethods
@@ -26,3 +27,4 @@ module Pacemaker
       end
     end
   end
+end

libraries/pacemaker/resource/group.rb

@@ -5,7 +5,7 @@ class Pacemaker::Resource::Group < Pacemaker::Resource
   TYPE = 'group'
   register_type TYPE
 
-  include Pacemaker::Resource::Meta
+  include Pacemaker::Mixins::Resource::Meta
 
   attr_accessor :members
 

libraries/pacemaker/resource/primitive.rb

@@ -6,7 +6,7 @@ class Pacemaker::Resource::Primitive < Pacemaker::Resource
   TYPE = 'primitive'
   register_type TYPE
 
-  include Pacemaker::Resource::Meta
+  include Pacemaker::Mixins::Resource::Meta
 
   attr_accessor :agent, :params, :op