[SPARK-15659][SQL] Ensure FileSystem is gotten from path

## What changes were proposed in this pull request?

Currently `spark.sql.warehouse.dir` is pointed to local dir by default, which will throw exception when HADOOP_CONF_DIR is configured and default FS is hdfs.

```
java.lang.IllegalArgumentException: Wrong FS: file:/Users/sshao/projects/apache-spark/spark-warehouse, expected: hdfs://localhost:8020
```

So we should always get the `FileSystem` from `Path` to avoid wrong FS problem.

## How was this patch tested?

Local test.

Author: jerryshao <sshao@hortonworks.com>

Closes #13405 from jerryshao/SPARK-15659.