Prevent re-running sensu::check every puppet run

Similar to j-russell's commit, updated occurrences, low_flap_threshold,
high_flap_threshold attributes, setting them to_s to prevent refreshes on
every run

lib/puppet/provider/sensu_check/json.rb

@@ -147,23 +147,23 @@ def refresh=(value)
   end
 
   def occurrences
-    conf['checks'][resource[:name]]['occurrences']
+    conf['checks'][resource[:name]]['occurrences'].to_s
   end
 
   def occurrences=(value)
     conf['checks'][resource[:name]]['occurrences'] = value.to_i
   end
 
   def low_flap_threshold
-    conf['checks'][resource[:name]]['low_flap_threshold']
+    conf['checks'][resource[:name]]['low_flap_threshold'].to_s
   end
 
   def low_flap_threshold=(value)
     conf['checks'][resource[:name]]['low_flap_threshold'] = value.to_i
   end
 
   def high_flap_threshold
-    conf['checks'][resource[:name]]['high_flap_threshold']
+    conf['checks'][resource[:name]]['high_flap_threshold'].to_s
   end
 
   def high_flap_threshold=(value)