repositories.hdfs.path can not be set

[dadoonet]

Reported at: https://discuss.elastic.co/t/combine-elasticsearch-5-1-1-and-repository-hdfs/69659

If you define as described in our docs the following elasticsearch.yml settings:

repositories:
  hdfs:
    uri: "hdfs://es-master:9000/" # optional - Hadoop file-system URI
    path: "some/path" # required - path with the file-system where data is stored/loaded

It fails at startup because we don't register the global setting repositories.hdfs.path in HdfsPlugin.

We should either support all global repositories.hdfs settings we documented or remove that from our docs so people must provide those settings only when registering the repository with:

PUT _snapshot/my_hdfs_repository
{
  "type": "hdfs",
  "settings": {
    "uri": "hdfs://namenode:8020/",
    "path": "elasticsearch/respositories/my_hdfs_repository",
    "conf.dfs.client.read.shortcircuit": "true"
  }
}

[dadoonet]

@jbaiera I can fix it but I'd like to know what is your point of view on the above ^^^

[dadoonet]

@jbaiera ping :) Would love to have your opinion.

[jbaiera]

@dadoonet I think that registering the configurations would be the more sensible course of action. I'm happy to open a PR for it soon.

[dadoonet]

@jbaiera actually I think that based on discussion we had with @rjernst about s3 plugin I think we should better get rid of repositories.impl settings totally (see #22800). It makes the code a way too much complex for a very little gain.

I'm going to open a PR about removing that from the documentation instead and we can discuss about it there (or here).

[jbaiera]

@dadoonet I'm fine with this course of action. I think it makes sense if the general consensus is to move away from the pattern. Thanks much!