[SPARK-20119][TEST-MAVEN] Fix the test case fail in DataSourceScanExecRedactionSuite

### What changes were proposed in this pull request?
Changed the pattern to match the first n characters in the location field so that the string truncation does not affect it.

### How was this patch tested?
N/A

Author: Xiao Li <gatorsmile@gmail.com>

Closes #17448 from gatorsmile/fixTestCAse.

sql/core/src/test/scala/org/apache/spark/sql/execution/DataSourceScanExecRedactionSuite.scala

@@ -31,7 +31,7 @@ class DataSourceScanExecRedactionSuite extends QueryTest with SharedSQLContext {
 
   override def beforeAll(): Unit = {
     sparkConf.set("spark.redaction.string.regex",
-      "spark-[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12}")
+      "file:/[\\w_]+")
     super.beforeAll()
   }