Core: improve build_release.py

Don't insist on log file removal until after usage is printed.

Some simple Python code improvements (x.find(y) != -1 --> y in x)

Make sure the git area is "clean" (has no unpushed changes, has pulled
all changes, has no untracked files)

Add label color detail when creating next github version label.

Closes #7913
release tool: fix 'log exists' check to not create the log before it checks ;)
Docs: Fixed issue link in doc values section of resiliency status
Mappings: Make lookup structures immutable.

This commit makes the lookup structures that are used for mappings immutable.
When changes are required, a new instance is created while the current instance
is left unmodified. This is done efficiently thanks to a hash table
implementation based on a array hash trie, see
org.elasticsearch.common.collect.CopyOnWriteHashMap.

ManyMappingsBenchmark returns indexing times that are similar to the ones that
can be observed in current master.

Ultimately, I would like to see if we can make mappings completely immutable as
well and updated atomically. This is not trivial however, eg. because of dynamic
mappings. So here is a first baby step that should help move towards that
direction.

Close #7486
DiscoveryWithServiceDisruptions: some more java docs and todos
release tool: must decode bytes to string
Discovery: only accept unicast pings when started

Due to component start order we may process an incoming ping while the ZenDiscovery module is not yet started. This leads to exception (from which we recover correctly, but the logs are note nice). UnicastZenPing should only start processing pings if it is started. We previously processed if not closed or stopped.

Closes #7950
Discovery: add a finalize round to multicast pinging

When sending a multicast ping, there is no way to determine how long it will take before all nodes will respond. Currently we send two pings (one at start, one after half timeout) and wait until the ping timeout has passed for all responses to come back. However, if all nodes are fast to respond, there is a gap relatively large between the moment that pings were gathered and the election that is based on them. This commits adds a last ping round (at timeout) where we know the number of nodes we expect to receive answers from. Once all nodes responded, we complete the pinging.

Closes #7924
Docs: Updated the resiliency docs to point to the DiscoveryWithServiceDisruptions class
Upgrade to Jackson 2.4.2
closes #7934
closes #7932
Logging: suppress long mapping logging during mapping updates (unless in TRACE)

Currently DEBUG logs can get very verbose because IndicesClusterStateService logs the complete mapping with every mapping update. We should suppress it if long in DEBUG mode and always log the full one in TRACE.

Closes #7949
Term Vectors: support for realtime

By default term vectors are now realtime, as opposed to previously near
realtime. If they are not found in the index, they will be generated on the
fly. The document is fetched from the transaction log and treated as an
artificial document. One can set `realtime` parameter to `false` in order to
disable this functionality. This consequently makes the MLT query realtime in
fetching documents, as it previsouly used to be before switching from using
the multi get API to the mtv API.

Closes #7846
Tests: Add more assertions to ExistsMissingTests.
Internal: Don't let `took` be negative.

`took` is computed based on the system clock and can be negative if the clock
time was updated during the execution of the search request. This commit
protects against these cases by replacing `took` with 1 if the elapsed time is
negative.

Close #7968
Admin: show open and closed indices in _cat/indices

When asking for `GET /_cat/indices?v`, you can now retrieve closed indices in addition to opened ones.

```
health status index              pri rep docs.count docs.deleted store.size pri.store.size
yellow open   .marvel-2014.05.21   1   1       8792            0     21.7mb         21.7mb
       close  test
yellow open   .marvel-2014.05.22   1   1       3871            0     10.7mb         10.7mb
red    open   .marvel-2014.05.27   1   1
```

Closes #7907.
Closes #7936.
Aggs fix - background count for docs should include deleted docs otherwise a term’s docFreq (which includes deleted docs) can exceed the number of docs reported in the index and cause an exception.
The randomisation that deletes documents is also removed from tests as this doc-accounting change would mean the specific scores being expected in tests would now be subject to random variability and so fail.

Closes #7951
Tests: Improve BWC preconditions to error cleanly when wire formats differ.

closes #7966
Term Vectors/MLT Query: support for different analyzers than default at field

This adds a `per_field_analyzer` parameter to the Term Vectors API, which
allows to override the default analyzer at the field. If the field already
stores term vectors, then they will be re-generated. Since the MLT Query uses
the Term Vectors API under its hood, this commits also adds the same ability
to the MLT Query, thereby allowing users to fine grain how each field item
should be processed and analyzed.

Closes #7801
Fix NPE in ScriptService when script file with no extension is deleted

Fixes #7689
Snapshot/Restore: Make sure indices cannot be renamed into restored aliases

Fixes #7915