Avoid to use Random.nextString in StreamingInnerJoinSuite

Author: HyukjinKwon

sql/core/src/test/scala/org/apache/spark/sql/streaming/StreamingJoinSuite.scala

@@ -350,7 +350,7 @@ class StreamingInnerJoinSuite extends StreamTest with StateStoreMetricsTest with
     withTempDir { tempDir =>
       val queryId = UUID.randomUUID
       val opId = 0
-      val path = Utils.createDirectory(tempDir.getAbsolutePath, Random.nextString(10)).toString
+      val path = Utils.createDirectory(tempDir.getAbsolutePath, Random.nextFloat.toString).toString
       val stateInfo = StatefulOperatorStateInfo(path, queryId, opId, 0L, 5)
 
       implicit val sqlContext = spark.sqlContext