SOLR-14238: Fix HdfsDirectory to no longer overwrite existing files.

[jpountz]

No description provided.

[risdenk]

@jpountz thanks. Change looks reasonable. I'm assuming this is due to the contract for a directory? I can run through the hdfs tests in a few hours.

[jpountz]

@risdenk Correct. I'd also like to add support for createTempOutput in a follow-up change. The lack of support for it in HdfsDirectory means Solr tests don't pass on my other pull request #1179, and one way to make it work would be to generate temporary file names until creating a file with this name doesn't throw a FileAlreadyExistsException, like we do in FSDirectory.

[jpountz]

Thanks @risdenk !