[SPARK-21016][CORE] Improve code fault tolerance for converting string to number

## What changes were proposed in this pull request?
When converting `string` to `number`(int, long or double),  if the string has a space before or after,will lead to unnecessary mistakes.

## How was this patch tested?
unit test

Author: liuxian <liu.xian3@zte.com.cn>

Closes #18238 from 10110346/lx-wip-0608.

core/src/main/scala/org/apache/spark/internal/config/ConfigBuilder.scala

@@ -28,7 +28,7 @@ private object ConfigHelpers {
 
   def toNumber[T](s: String, converter: String => T, key: String, configType: String): T = {
     try {
-      converter(s)
+      converter(s.trim)
     } catch {
       case _: NumberFormatException =>
         throw new IllegalArgumentException(s"$key should be $configType, but was $s")
@@ -37,7 +37,7 @@ private object ConfigHelpers {
 
   def toBoolean(s: String, key: String): Boolean = {
     try {
-      s.toBoolean
+      s.trim.toBoolean
     } catch {
       case _: IllegalArgumentException =>
         throw new IllegalArgumentException(s"$key should be boolean, but was $s")

sql/core/src/test/scala/org/apache/spark/sql/internal/SQLConfEntrySuite.scala

@@ -37,6 +37,9 @@ class SQLConfEntrySuite extends SparkFunSuite {
     assert(conf.getConfString(key) === "20")
     assert(conf.getConf(confEntry, 5) === 20)
 
+    conf.setConfString(key, " 20")
+    assert(conf.getConf(confEntry, 5) === 20)
+
     val e = intercept[IllegalArgumentException] {
       conf.setConfString(key, "abc")
     }
@@ -75,6 +78,8 @@ class SQLConfEntrySuite extends SparkFunSuite {
     assert(conf.getConfString(key) === "true")
     assert(conf.getConf(confEntry, false) === true)
 
+    conf.setConfString(key, " true ")
+    assert(conf.getConf(confEntry, false) === true)
     val e = intercept[IllegalArgumentException] {
       conf.setConfString(key, "abc")
     }