ini_setting: Skip transformer if value is not changed

... so that we can create a resource with value = nil and no
transformers.

This is required to fix the problem with puppet-swift which requires
to manage sections without any values.

Change-Id: I7ece6da0e16b275faf4120baf0ff68970491dc9d

lib/puppet/provider/openstack_config/ini_setting.rb

@@ -20,7 +20,10 @@ Puppet::Type.type(:openstack_config).provide(
   end
 
   def create
-    resource[:value] = transform(:to, resource[:value])
+    new_value = transform(:to, resource[:value])
+    if resource[:value] != new_value
+      resource[:value] = new_value
+    end
     super
   end