[sensu_check] fix conditional validation of subscribers/standalone (#547

)

* [sensu_check] fix conditional validation of required subscribers/standalone attribute
* [sensu_check] ensure action is an array before checking for :create

resources/check.rb

@@ -23,7 +23,7 @@ def after_created
     raise Chef::Exceptions::ValidationFailed, "Sensu check #{name}: name cannot contain spaces or special characters"
   end
 
-  if action == :create
+  if [action].compact.flatten.include?(:create)
      raise Chef::Exceptions::ValidationFailed, "Sensu check #{name}: must either define subscribers, or has to be standalone." unless (subscribers || standalone)
   end
 end