[SPARK-20553][ML][PYSPARK] Update ALS examples with recommend-all methods

Update ALS examples illustrating use of "recommendForAllX" methods.

## How was this patch tested?
Built and ran examples locally

Author: Nick Pentreath <nickp@za.ibm.com>

Closes #17950 from MLnick/SPARK-20553-update-als-examples.

examples/src/main/java/org/apache/spark/examples/ml/JavaALSExample.java

@@ -113,7 +113,15 @@ public class JavaALSExample {
       .setPredictionCol("prediction");
     Double rmse = evaluator.evaluate(predictions);
     System.out.println("Root-mean-square error = " + rmse);
+
+    // Generate top 10 movie recommendations for each user
+    Dataset<Row> userRecs = model.recommendForAllUsers(10);
+    // Generate top 10 user recommendations for each movie
+    Dataset<Row> movieRecs = model.recommendForAllItems(10);
     // $example off$
+    userRecs.show();
+    movieRecs.show();
+    
     spark.stop();
   }
 }

examples/src/main/python/ml/als_example.py

@@ -55,5 +55,13 @@ if __name__ == "__main__":
                                     predictionCol="prediction")
     rmse = evaluator.evaluate(predictions)
     print("Root-mean-square error = " + str(rmse))
+
+    # Generate top 10 movie recommendations for each user
+    userRecs = model.recommendForAllUsers(10)
+    # Generate top 10 user recommendations for each movie
+    movieRecs = model.recommendForAllItems(10)
     # $example off$
+    userRecs.show()
+    movieRecs.show()
+
     spark.stop()

examples/src/main/scala/org/apache/spark/examples/ml/ALSExample.scala

@@ -75,7 +75,14 @@ object ALSExample {
       .setPredictionCol("prediction")
     val rmse = evaluator.evaluate(predictions)
     println(s"Root-mean-square error = $rmse")
+
+    // Generate top 10 movie recommendations for each user
+    val userRecs = model.recommendForAllUsers(10)
+    // Generate top 10 user recommendations for each movie
+    val movieRecs = model.recommendForAllItems(10)
     // $example off$
+    userRecs.show()
+    movieRecs.show()
 
     spark.stop()
   }