[UTILITIES] Introduce a RefCounted interface and basic impl

We already have two places duplicating this rather hairy logic, this
commit intorduces a new RefCoutned interace and an abstract implementation
that can be used for delegation. It factors out all the reference counting
and adds single and multithreaded test for it.

Closes #8210
[CACHE] Expose concurrency_level on all caches

The concurrency level allows to configure the cache internal segments
used to cache data. This can have direct impact on evicition rates since
memory bound caches are equally divided into segments which can cause
early evictions if cache entries are not well balanced.

Relates to #7836
[STORE] Don't catch FNF/NSF exception when reading metadata

When reading metadata we do catch FileNotFound and NoSuchFileExceptions
today, log the even and return an empty metadata object. Yet, in some cases
this might be the wrong thing todo ie. if a commit point is provided these
situations are actually an error and should be rethrown. This commit
pushes the responsiblity to the caller to handle this exception.

Closes #8207
Term Vectors: removed Nullable annotation on a primitive type
ParseField: Support for when all fields are deprecated

Closes #8067
Bulk indexing: Fix 8125 hanged request when auto create index is off.
If a bulk request contains a mix of indexing requests for an existing index and one that needs to be auto-created but a cluster configuration prevents the auto-create of the new index the ingest process hangs. The exception for the failure to create an index was not caught or reported back properly. Added a Junit test to recreate the issue and the associated fix is in TransportBulkAction.

Closes #8125
Docs: fixed typo in documentation

Closes #8205
Docs: rolling upgrade process seems incorrect

When reading the [rolling upgrade process](http://www.elasticsearch.org/guide/en/elasticsearch/reference/current/setup-upgrade.html#rolling-upgrades), you can see that we wrote:

* disable allocation
* upgrade node1
* upgrade node2
* upgrade node3
* ...
* enable allocation

That won't work as after a node has been removed and restarted, no shard will be allocated anymore.
So closing node2 and remaining nodes, won't help to serve index and search request anymore.

We should write:

* disable allocation
* upgrade node1
* enable allocation
* wait for shards being recovered on node1
* disable allocation
* upgrade node2
* enable allocation
* wait for shards being recovered on node2
* disable allocation
* upgrade node3
* enable allocation
* wait for shards being recovered on node3
* disable allocation
* ...
* enable allocation

I think this documentation update should go in 1.3, 1.4, 1.x and master branches.

Closes #8218
Closes #7973.
Catch both FileNotFound & NoSuchFileException
MLT Query: versatile 'like' parameter

The MLT query has a lot of parameters. For example, a set of documents is
specified with either `like_text`, `ids` or `docs`, with at least one
parameter required. This commit groups all the document specification
parameters under one called `like`. The syntax is described below and could
easily be extended to allow for new means of specifying document input. The
`like_text`, `ids` and `docs` parameters are deprecated.

As a single piece text:

{
  "query": {
    "more_like_this": {
      "like": "some text here"
    }
  }
}

As a single item:

{
  "query": {
    "more_like_this": {
      "like": {
        "_index": "imdb",
        "_type": "movies",
        "_id": "88247"
      }
    }
  }
}

Or as a mixture of all:

{
  "query": {
    "more_like_this": {
      "like": [
        "Some random text ...",
        {
          "_index": "imdb",
          "_type": "movies",
          "_id": "88247"
        },
        {
          "_index": "imdb",
          "_type": "movies",
          "doc": {
            "title": "Document with an artificial title!"
          }
        }
      ]
    }
  }
}

Closes #8039
Test: testRecoverFromPreviousVersion should refresh from new nodes if running against v<1.3.0

This is due to a bug in older version causing refreshes to potentially be missed due to relocations #6545

Also:
- Changed test to keep track of ids and report missing ones.
- Removed total count check from assertSearchHits in order to enable per id checks in cased of a mismatch
- Added a printable unique id part the ids of dummy documents added by indexRandom. The current random unicode id
sometimes prints as ???? to the logs making them hard to trace
[TEST] `Scope.SUITE` is not reproducible due to late cluster initialization

The cluster for `Scope.SUITE` tests must be initialize in a static manner
before the first test runs otherwise the random context used to initialize
the cluster is taken from tests randomness rather than the suites randomness.
This means test clusters will have different setups if only a single test is
executed or even the test might have a entirely different random sequence.
add missing imports
[TEST] NettyTransportMultiPortIntegrationTests used wrong random to
initialize ports.

JUnit uses an instance per test which caused the prot range to be
initialized twice since suite level tests are not configured in a
different context.
Recovery: RecoveriesCollection.findRecoveryByShard should call recoveryStatus.tryIncRef before accessing fields

The function iterates over a snapshot of on going recoveries and thus may access RecoveryStatus objects that are already finished.

Closes #8231
Core: Validates bool values in yaml for node settings

- Added parseBooleanExact in booleans which throws exception in case of
  parse failure
- Used ParseExact in static's to make it consistent

+ code review fixes

- Added unit test
- Changed Exception Type to ElasticSearchIllegalArg from Parse
- used isExplicit*

Closes #8097
[TEST] Add test for #8226
Cat API: Add node name to _cat/recovery

Add source_node and target_node fields to the recovery cat API. Also fixed and updated the documentation which was not complete concerning fields names.

Closes #8041
[TESTS Fix wrong assertion in test introduced by #8128
Aggregations: Return the sum of the doc counts of other buckets.

This commit adds a new field to the response of the terms aggregation called
`sum_other_doc_count` which is equal to the sum of the doc counts of the buckets
that did not make it to the list of top buckets. It is typically useful to have
a sector called eg. `other` when using terms aggregations to build pie charts.

Example query and response:

```json
GET test/_search?search_type=count
{
  "aggs": {
    "colors": {
      "terms": {
        "field": "color",
        "size": 3
      }
    }
  }
}
```

```json
{
   [...],
   "aggregations": {
      "colors": {
         "doc_count_error_upper_bound": 0,
         "sum_other_doc_count": 4,
         "buckets": [
            {
               "key": "blue",
               "doc_count": 65
            },
            {
               "key": "red",
               "doc_count": 14
            },
            {
               "key": "brown",
               "doc_count": 3
            }
         ]
      }
   }
}
```

Close #8213