Spark streaming deletes the temp file and backup files without checking if they exist or not

Author: Hao Zhu <viadeazhu@gmail.com>

Closes #8082 from viadea/master and squashes the following commits:

242d05f [Hao Zhu] [SPARK-9801][Streaming]No need to check the existence of those files
fd143f2 [Hao Zhu] [SPARK-9801][Streaming]Check if backupFile exists before deleting backupFile files.
087daf0 [Hao Zhu] SPARK-9801