[SPARK-5780] [PySpark] Mute the logging during unit tests

There a bunch of logging coming from driver and worker, it's noisy and scaring, and a lots of exception in it, people are confusing about the tests are failing or not.

This PR will mute the logging during tests, only show them if any one failed.

Author: Davies Liu <davies@databricks.com>

Closes #4572 from davies/mute and squashes the following commits:

1e9069c [Davies Liu] mute the logging during python tests

python/run-tests

@@ -35,7 +35,7 @@ rm -rf metastore warehouse
 function run_test() {
     echo "Running test: $1" | tee -a $LOG_FILE
 
-    SPARK_TESTING=1 time "$FWDIR"/bin/pyspark $1 2>&1 | tee -a $LOG_FILE
+    SPARK_TESTING=1 time "$FWDIR"/bin/pyspark $1 >> $LOG_FILE 2>&1
 
     FAILED=$((PIPESTATUS[0]||$FAILED))