Ignore stores image property

Currently Glance includes "stores" image property automatically in
image show API. This property is assigned at api side and client
is not allowed to update the value.

This change ensures that the property is ignored to prevent
the glance_image resource from detecting false change because of that
read-only property.

Change-Id: I0242f13402a56cf898439fa6b0b3972da38dbebb

lib/puppet/provider/glance_image/openstack.rb

@@ -175,7 +175,7 @@ Puppet::Type.type(:glance_image).provide(
     if props == nil
       return nil
     end
-    hidden = ['os_hash_algo', 'os_hash_value', 'os_hidden']
+    hidden = ['os_hash_algo', 'os_hash_value', 'os_hidden', 'stores']
     rv = props.select { |k, v| not hidden.include?(k) }
     return rv
   end