[SPARK-3527] [SQL] Strip the string message

Author: Cheng Hao <hao.cheng@intel.com>

Closes #2392 from chenghao-intel/trim and squashes the following commits:

e52024f [Cheng Hao] trim the string message

sql/core/src/main/scala/org/apache/spark/sql/SQLContext.scala

@@ -414,7 +414,7 @@ class SQLContext(@transient val sparkContext: SparkContext)
     def simpleString: String =
       s"""== Physical Plan ==
          |${stringOrError(executedPlan)}
-      """
+      """.stripMargin.trim
 
     override def toString: String =
       // TODO previously will output RDD details by run (${stringOrError(toRdd.toDebugString)})