more robust updating of custom pcs properties

Added the function update_my_node_property_verified which makes use of the already existing update_my_node_property function.  This is more robust -- we want to make sure the property update sticks (I believe I saw a case in development recently where it did not... bad things ensue).

Note that if called from the command line there would be the potential for an infinite loop, however this is not the case when called from a puppet exec where a "timeout" exists.  I.e., it should be up to puppet how long the command should attempt to update the property before giving up.

Tested.