Fix for ttl fieldmapper to support disabling correctly. Also returning only booleans, not enums in toXContent
Returning configuration of root field mappers toXContent method only if they are enabled
Cleanup ScriptDocValues. This commit adds a getValues method to all ScriptDocValues for easy access
in scripts via doc['field'].values / value.
Settings / Config: Allow to explicitly specify external environment variable syntax, in which case its optional
fixes #2855
Catch Throwable when listener is called rather then Exception to prevent possible hangs if fatal exceptions or errors are thrown
Thread Pool: Update default settings (move from default cached to fixed)
closes #2858
allow to disable the optimization of removal of ords on single value numerics/geo field data
field data settings in the mappings can have ordinals=always option
Added test that compares concurrent facet execution results with a serial execution result
beef up term facet tests
List of existing plugins with Node Info API
We want to display information about loaded plugins in Node Info API using plugin option:

```sh
curl http://localhost:9200/_nodes?plugin=true
```

For example, on a 4 nodes cluster, it could provide the following output:

```javascript
{
  "ok" : true,
  "cluster_name" : "test-cluster-MacBook-Air-de-David.local",
  "nodes" : {
    "lodYfbFTRnmwE6rjWGGyQQ" : {
      "name" : "node1",
      "transport_address" : "inet[/172.18.58.139:9300]",
      "hostname" : "MacBook-Air-de-David.local",
      "version" : "0.90.0.Beta2-SNAPSHOT",
      "http_address" : "inet[/172.18.58.139:9200]",
      "plugins" : [ ]
    },
    "hJLXmY_NTrCytiIMbX4_1g" : {
      "name" : "node4",
      "transport_address" : "inet[/172.18.58.139:9303]",
      "hostname" : "MacBook-Air-de-David.local",
      "version" : "0.90.0.Beta2-SNAPSHOT",
      "http_address" : "inet[/172.18.58.139:9203]",
      "plugins" : [ {
        "name" : "test-plugin",
        "description" : "test-plugin description",
        "site" : true,
        "jvm" : false
      }, {
        "name" : "test-no-version-plugin",
        "description" : "test-no-version-plugin description",
        "site" : true,
        "jvm" : false
      }, {
        "name" : "dummy",
        "description" : "No description found for dummy.",
        "url" : "/_plugin/dummy/",
        "site" : false,
        "jvm" : true
      } ]
    },
    "bnoySsBfTrSzbDRZ0BFHvg" : {
      "name" : "node2",
      "transport_address" : "inet[/172.18.58.139:9301]",
      "hostname" : "MacBook-Air-de-David.local",
      "version" : "0.90.0.Beta2-SNAPSHOT",
      "http_address" : "inet[/172.18.58.139:9201]",
      "plugins" : [ {
        "name" : "dummy",
        "description" : "This is a description for a dummy test site plugin.",
        "url" : "/_plugin/dummy/",
        "site" : false,
        "jvm" : true
      } ]
    },
    "0Vwil01LSfK9YgRrMce3Ug" : {
      "name" : "node3",
      "transport_address" : "inet[/172.18.58.139:9302]",
      "hostname" : "MacBook-Air-de-David.local",
      "version" : "0.90.0.Beta2-SNAPSHOT",
      "http_address" : "inet[/172.18.58.139:9202]",
      "plugins" : [ {
        "name" : "test-plugin",
        "description" : "test-plugin description",
        "site" : true,
        "jvm" : false
      } ]
    }
  }
}
```

Information are cached for 10 seconds by default. Modify `plugins.info_refresh_interval` property if needed.
Setting `plugins.info_refresh_interval` to `-1` will cause infinite caching.
Setting `plugins.info_refresh_interval` to `0` will disable caching.

Closes #2668.
Initial `all_terms` implementation. Triggered when:
* The `fields` option is used
* The `map` `execution_type` is used
* The `field` used is a number based field.
Moved term loading to constructor
Added optimisation in case actual field is ordinal based (in case hint='map' or fields option is used)