Checks for ElasticSearch 0.9x and 1.x

/_cluster/nodes/_local has been retired with ES 1.0, so this check does
not work anymore.
By identifying the cluster version before running the check,
we can adjust the URL.

plugins/elasticsearch/check-es-cluster-status.rb

@@ -5,6 +5,7 @@
 #
 # DESCRIPTION:
 #   This plugin checks the ElasticSearch cluster status, using its API.
+#   Works with ES 0.9x and ES 1.x
 #
 # OUTPUT:
 #   plain-text
@@ -45,10 +46,20 @@ def get_es_resource(resource)
     end
   end
 
+  def version
+    info = get_es_resource('/')
+    info['version']['number']
+  end
+
   def is_master
-    state = get_es_resource('/_cluster/state?filter_routing_table=true&filter_metadata=true&filter_indices=true')
-    local = get_es_resource('/_cluster/nodes/_local')
-    local['nodes'].keys.first == state['master_node']
+    if Gem::Version.new(version) >= Gem::Version.new('1.0.0')
+      master = get_es_resource('_cluster/state/master_node')['master_node']
+      local = get_es_resource('/_nodes/_local')
+    else
+      master = get_es_resource('/_cluster/state?filter_routing_table=true&filter_metadata=true&filter_indices=true')['master_node']
+      local = get_es_resource('/_cluster/nodes/_local')
+    end
+    local['nodes'].keys.first == master
   end
 
   def get_status