[XPACK] Update tests for changed xpack paths

Author: estolfo

elasticsearch-xpack/test/unit/graph/explore_test.rb

@@ -27,7 +27,7 @@ class GraphExploreTest < Minitest::Test
         should "perform correct request" do
           subject.expects(:perform_request).with do |method, url, params, body|
             assert_equal 'GET', method
-            assert_equal '_xpack/_graph/_explore', url
+            assert_equal '_graph/explore', url
             assert_equal Hash.new, params
             assert_equal nil, body
             true

elasticsearch-xpack/test/unit/machine_learning/delete_forecast_test.rb

@@ -10,7 +10,7 @@ class XPackMlDeleteForecastTest < Minitest::Test
         should "perform correct request" do
           subject.expects(:perform_request).with do |method, url, params, body|
             assert_equal 'DELETE', method
-            assert_equal "_xpack/ml/anomaly_detectors/foo/_forecast/", url
+            assert_equal "_ml/anomaly_detectors/foo/_forecast/", url
             assert_equal Hash.new, params
             assert_nil   body
             true