Plugin Manager can now use another simplified form when a user wants to install an official plugin hosted at elasticsearch download service.
The form we use is:
```sh
bin/plugin install pluginname
```
As plugins share now the same version as elasticsearch, we can automatically guess what is the exact current version of the plugin manager script.
Also, download service will now use `/org.elasticsearch.plugins/pluginName/pluginName-version.zip` URL path to download a plugin.
If the older form is provided (`user/plugin/version` or `user/plugin`), we will still use:
* elasticsearch download service at `/user/plugin/plugin-version.zip`
* maven central with groupIp=user, artifactId=plugin and version=version
* github with user=user, repoName=plugin and tag=version
* github with user=user, repoName=plugin and branch=master if no version is set
Note that community plugin providers can use other download services by using `--url` option.
If you try to use the new form with a non core elasticsearch plugin, the plugin manager will reject
it and will give you all known core plugins.
```
Usage:
-u, --url [plugin location] : Set exact URL to download the plugin from
-i, --install [plugin name] : Downloads and installs listed plugins [*]
-t, --timeout [duration] : Timeout setting: 30s, 1m, 1h... (infinite by default)
-r, --remove [plugin name] : Removes listed plugins
-l, --list : List installed plugins
-v, --verbose : Prints verbose messages
-s, --silent : Run in silent mode
-h, --help : Prints this help message
[*] Plugin name could be:
elasticsearch-plugin-name for Elasticsearch 2.0 Core plugin (download from download.elastic.co)
elasticsearch/plugin/version for elasticsearch commercial plugins (download from download.elastic.co)
groupId/artifactId/version for community plugins (download from maven central or oss sonatype)
username/repository for site plugins (download from github master)
Elasticsearch Core plugins:
- elasticsearch-analysis-icu
- elasticsearch-analysis-kuromoji
- elasticsearch-analysis-phonetic
- elasticsearch-analysis-smartcn
- elasticsearch-analysis-stempel
- elasticsearch-cloud-aws
- elasticsearch-cloud-azure
- elasticsearch-cloud-gce
- elasticsearch-delete-by-query
- elasticsearch-lang-javascript
- elasticsearch-lang-python
```
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