If node can't handle this action, put it back to available node list,…

… so it can handle another action.

lib/cloud_crowd/models/work_unit.rb

@@ -54,6 +54,7 @@ def self.distribute_to_nodes
             unit.cancel_reservation
           end
           work_units.push(unit)
+          available_nodes.push(node)
         end
         if work_units.any? && available_nodes.any?
           filter = {:action => available_nodes.map {|node| node.actions }.flatten.uniq }