[SPARK-19677][SS] Committing a delta file atop an existing one should not fail on HDFS

## What changes were proposed in this pull request?

HDFSBackedStateStoreProvider fails to rename files on HDFS but not on the local filesystem. According to the [implementation notes](https://hadoop.apache.org/docs/stable/hadoop-project-dist/hadoop-common/filesystem/filesystem.html

) of `rename()`, the behavior of the local filesystem and HDFS varies:

> Destination exists and is a file
> Renaming a file atop an existing file is specified as failing, raising an exception.
>    - Local FileSystem : the rename succeeds; the destination file is replaced by the source file.
>    - HDFS : The rename fails, no exception is raised. Instead the method call simply returns false.

This patch ensures that `rename()` isn't called if the destination file already exists. It's still semantically correct because Structured Streaming requires that rerunning a batch should generate the same output.

## How was this patch tested?

This patch was tested by running `StateStoreSuite`.

Author: Roberto Agostino Vitillo <ra.vitillo@gmail.com>

Closes #17012 from vitillo/fix_rename.

(cherry picked from commit 9734a928)
Signed-off-by: Shixiong Zhu <shixiong@databricks.com>