[TEST] Reduce number of updates and wait after 1st NoNodeException.
Generate timestamp when path is null

Index process fails when having `_timestamp` enabled and `path` option is set.
It fails with a `TimestampParsingException[failed to parse timestamp [null]]` message.

Reproduction:

```
DELETE test
PUT  test
{
    "mappings": {
        "test": {
            "_timestamp" : {
                "enabled" : "yes",
                "path" : "post_date"
            }
        }
    }
}
PUT test/test/1
{
  "foo": "bar"
}
```

You can define a default value for when timestamp is not provided
within the index request or in the `_source` document.

By default, the default value is `now` which means the date the document was processed by the indexing chain.

You can disable that default value by setting `default` to `null`. It means that `timestamp` is mandatory:

```
{
    "tweet" : {
        "_timestamp" : {
            "enabled" : true,
            "default" : null
        }
    }
}
```

If you don't provide any timestamp value, indexation will fail.

You can also set the default value to any date respecting timestamp format:

```
{
    "tweet" : {
        "_timestamp" : {
            "enabled" : true,
            "format" : "YYYY-MM-dd",
            "default" : "1970-01-01"
        }
    }
}
```

If you don't provide any timestamp value, indexation will fail.

Closes #4718.
Closes #7036.
Search Exists API: Checks if any matching documents exist for a given query

Implements a new Exists API allowing users to do fast exists check on any matched documents for a given query.
This API should be faster then using the Count API as it will:
 - early terminate the search execution once any document is found to exist
 - return the response as soon as the first shard reports matched documents

closes #6995
Mappings: Fix `copy_to` behavior on nested documents.

Today, `copy_to` always copies a field to the current document, which is often
wrong in the case of nested documents. For example, if you have a nested field
called `n` which has a sub-field `n.source` whose content should be copied to
`target`, then the latter field should be created in the root document instead
of the nested one, since it doesn't have `n.` as a prefix. On the contrary, if
you configure the destination field to be `n.target`, then it should go to the
nested document.

Close #6701
Aggregations: Fix infinite loop in the histogram reduce logic.

The histogram reduce method can run into an infinite loop if the
Rounding.nextRoundingValue value is buggy, which happened to be the case for
DayTimeZoneRoundingFloor.

DayTimeZoneRoundingFloor is fixed, and the histogram reduce method has been
changed to fail instead of running into an infinite loop in case of a buffy
nextRoundingValue impl.

Close #6965
Update fielddata-fields.asciidoc
Docs: add 1.4.0 label to many to many geo distance sort
[DOCS] fixed small typo in percolate.asciidoc
Function score query: Add missing whitespace when throwing exception

DecayFunctionParser throws a parse exception with a string containing "scaleand origin", this fixes the spacing issue.
Removed support for aliases as part of index settings

Now that we have explicit support for aliases when creating indices and as part of index templates, we may remove support for aliases (only names) as part of index settings. This is partially breaking as the following calls:

curl -XPUT localhost:9200/index -d '{
  "settings" : {
    "aliases" : [ "alias1"]
  }
}

and

curl -XPUT localhost:9200/index -d '{
  "settings" : {
    "index.aliases" : [ "alias1"]
  }
}

were previously supported and will need to be replaced with

curl -XPUT localhost:9200/index -d '{
  "aliases" : {
    "alias1": {}
  }
}

Closes #5545
[TEST] check breaker reset after parent trip instead of trip count
Sort: Make `ignore_unmapped` work for cross-index queries.

Close #2255
Aggregations Added Filters aggregation

A multi-bucket aggregation where multiple filters can be defined (each filter defines a bucket). The buckets will collect all the documents that match their associated filter.

This aggregation can be very useful when one wants to compare analytics between different criterias. It can also be accomplished using multiple definitions of the single filter aggregation, but here, the user will only need to define the sub-aggregations only once.

Closes #6118
[Fix] CompletionMapper throws misleading error on null value

closes #6399
Fix missing break statement causing reroute serialization failure
closes #7135
Added a cli infrastructure

CliTool is a base class for command-line interface tools (such as the plugin manager and potentially others). It supports the following:
  - single or multi command tool
  - help printing infrastructure (based on help files)
  - consistent mechanism of parsing arguments (based on commons-cli lib)
  - separation of argument parsing and command execution (for easier unit testing)
  - terminal abstraction (will use System.console() when available)
Support "default" for tcpNoDelay and tcpKeepAlive
Allow to set the value default to network.tcp.no_delay and network.tcp.keep_alive so they won't be set at all, since on solaris, setting tcpNoDelay can actually cause failure
relates to #7115
fixed platform independent line separator in CliToolTests
Added CliToolTestCase to the test jar
Added CliToolTestCase's sub classes to the test jar