[SPARK-14881] [PYTHON] [SPARKR] pyspark and sparkR shell default log level should match spark-shell/Scala

## What changes were proposed in this pull request?

Change default logging to WARN for pyspark shell and sparkR shell for a much cleaner environment.

## How was this patch tested?

Manually running pyspark and sparkR shell

Author: felixcheung <felixcheung_m@hotmail.com>

Closes #12648 from felixcheung/pylogging.

core/src/main/scala/org/apache/spark/api/python/PythonGatewayServer.scala

@@ -32,6 +32,8 @@ import org.apache.spark.util.Utils
  * This process is launched (via SparkSubmit) by the PySpark driver (see java_gateway.py).
  */
 private[spark] object PythonGatewayServer extends Logging {
+  initializeLogIfNecessary(true)
+
   def main(args: Array[String]): Unit = Utils.tryOrExit {
     // Start a GatewayServer on an ephemeral port
     val gatewayServer: GatewayServer = new GatewayServer(null, 0)

core/src/main/scala/org/apache/spark/api/r/RBackend.scala

@@ -94,6 +94,8 @@ private[spark] class RBackend {
 }
 
 private[spark] object RBackend extends Logging {
+  initializeLogIfNecessary(true)
+
   def main(args: Array[String]): Unit = {
     if (args.length < 1) {
       // scalastyle:off println
@@ -101,6 +103,7 @@ private[spark] object RBackend extends Logging {
       // scalastyle:on println
       System.exit(-1)
     }
+
     val sparkRBackend = new RBackend()
     try {
       // bind to random port