[TEST] Fix test issues with branches still using mvel as default scripting language
[TEST] Fix test relying on order of json for matching
Test: add diagnostics to get some details next time this test fails
Added more utility methods to Settings

- names() to return the direct settings names
- getAsSettings(String) to return the settings mapped to the given name (like getByPrefix(...) except no need to provide a tailing '.')
[TEST] close IW before listing directory content
Phrase Suggester: Add collate option to PhraseSuggester

The newly added collate option will let the user provide a template query/filter which will be executed for every phrase suggestions generated to ensure that the suggestion matches at least one document for the filter/query.
The user can also add routing preference `preference` to route the collate query/filter and additional `params` to inject into the collate template.

Closes #3482
[TEST] fix PhraseInIndex test bug for shard failure
[TEST] fix random preference string test to accomodate for the new more strict preference type
Stats: Expose IndexWriter and VersionMap RAM usage to ShardStats and _cat endpoint

This commit adds the RAM usage of IndexWriter and VersionMap

Closes #6483
[TEST] fix random preference string tests to accomodate for the new more strict preference type
[TEST] use higher timeout to wait for balanced cluster

CorruptFileTest sometimes hits conditions where lots of rebalancing
happens. In such a case the default timeout is just not enough - this
timeout just makes sure that the cluster has enough time to balance
itself.
Add version check before reading script type in UpdateRequest
Indexed Scripts/Templates: cleanup

This commit cleans up some code around the indexed script/templates feature.
Remove dead code in ScriptService.
Remove setXScript methods for UpdateRequestBuilder and use setScript(script,type) instead
Added missing version based serialization
[TEST] Fix test to use keyword analyzer since it relies on exact terms without processing
[SEARCH] Wrap filter only once in ApplyAcceptedDocsFilter

We potentially wrap the given filter multiple times when iterating the
subreaders. We only need to do this once.

Closes #6873
Core: don't close/reopen IndexWriter when changing RAM buffer size

Today we close/reopen IW when we change the RAM buffer but that's
costly because it means the next NRT reader is a full reopen.  The RAM
buffer size setting is a live one in IndexWriter, even if there are no
buffered docs in RAM when you call it.

Separately it would be nice if Lucene let you manage a "reader pool"
that could outlive individual IW instances ...

Closes #6856
Internal: make transport action name available in TransportAction base class

Each transport action is associated with at least an action name, which is the action name that gets serialized together with the request and identifies what to do with the request itself. Also, the action name is the name of the registered transport handler that handles incoming request for the transport action.

This commit makes the action name available in a generic manner in the TransportAction base class, so that it can be used when needed by subclasses, or in the base class for instance for action filtering.

Closes #6860
[UPDATE] Handle document missing exception on retry correctly.

Throwables thrown on update retries are now caught and handled via
the provided callback. This commit also contains an integration test
demonstrating the bug and validating the fix.

Closes #6355
Closes #6724
[TESTS] Add ElasticsearchSingleNodeTest.

This test makes it easy to create a lightweight node (no http, indices stored
in RAM, ...) whose main purpose is to get an instance of the Guice injector
for unit tests.

This should help not have to update lots of unit tests when we add a new
Guice dependency.