[SPARK-15025][SQL] fix duplicate of PATH key in datasource table options

## What changes were proposed in this pull request?
The issue is that when the user provides the path option with uppercase "PATH" key, `options` contains `PATH` key and will get into the non-external case in the following code in `createDataSourceTables.scala`, where a new key "path" is created with a default path.
```
val optionsWithPath =
      if (!options.contains("path")) {
        isExternal = false
        options + ("path" -> sessionState.catalog.defaultTablePath(tableIdent))
      } else {
        options
      }
```
So before creating hive table, serdeInfo.parameters will contain both "PATH" and "path" keys and different directories. and Hive table's dataLocation contains the value of "path".

The fix in this PR is to convert `options` in the code above to `CaseInsensitiveMap` before checking for containing "path" key.

## How was this patch tested?
A testcase is added

Author: xin Wu <xinwu@us.ibm.com>

Closes #12804 from xwu0226/SPARK-15025.