[API] Added the "Pending Tasks" API

Related: elastic/elasticsearch#3368

See: http://www.elasticsearch.org/guide/en/elasticsearch/reference/master/cluster-pending.html

elasticsearch-api/lib/elasticsearch/api/actions/cluster/pending_tasks.rb

@@ -0,0 +1,33 @@
+module Elasticsearch
+  module API
+    module Cluster
+      module Actions
+
+        # Returns a list of any cluster-level changes (e.g. create index, update mapping, allocate or fail shard)
+        # which have not yet been executed and are queued up.
+        #
+        # @example Get a list of currently queued up tasks in the cluster
+        #
+        #     client.cluster.pending_tasks
+        #
+        # @option arguments [Boolean] :local Return local information, do not retrieve the state from master node
+        #                                    (default: false)
+        # @option arguments [Time] :master_timeout Specify timeout for connection to master
+        #
+        # @see http://www.elasticsearch.org/guide/en/elasticsearch/reference/master/cluster-pending.html
+        #
+        def pending_tasks(arguments={})
+          valid_params = [
+            :local,
+            :master_timeout ]
+          method = 'GET'
+          path   = "/_cluster/pending_tasks"
+          params = Utils.__validate_and_extract_params arguments, valid_params
+          body   = nil
+
+          perform_request(method, path, params, body).body
+        end
+      end
+    end
+  end
+end

elasticsearch-api/test/unit/cluster/pending_tasks_test.rb

@@ -0,0 +1,26 @@
+require 'test_helper'
+
+module Elasticsearch
+  module Test
+    class ClusterPendingTasksTest < ::Test::Unit::TestCase
+
+      context "Cluster: Pending tasks" do
+        subject { FakeClient.new }
+
+        should "perform correct request" do
+          subject.expects(:perform_request).with do |method, url, params, body|
+            assert_equal 'GET', method
+            assert_equal '/_cluster/pending_tasks', url
+            assert_equal Hash.new, params
+            assert_nil   body
+            true
+          end.returns(FakeResponse.new)
+
+          subject.cluster.pending_tasks
+        end
+
+      end
+
+    end
+  end
+end