Test: CorruptedFileTest.testCorruptionOnNetworkLayer used node settings when creating an index

Test used `indices.recovery.concurrent_streams` when creating an index but this is a node setting. Moved it to the node settings and added similar settings to speed up concurrent recoveries.
Aggregations: Fix geohash grid aggregation on multi-valued fields.

This aggregation creates an anonymous fielddata instance that takes geo points
and turns them into a geo hash encoded as a long. A bug was introduced in 1.4
because of a fielddata refactoring: the fielddata instance tries to populate
an array with values without first making sure that it is large enough.

Close #8507
[root mappers] fix conflict when updating mapping with _all disabled

_all reports a conflict since #7377. However, it was not checked if _all
was actually configured in the updated mapping. Therefore whenever _all
was disabled a mapping could not be updated unless _all was again added to the
updated mapping.
Also, add enabled setting to mapping always whenever enabled was set explicitely.

closes #8423
closes #8426
Parser throws NullPointerException when Filter aggregation clause is empty.
Added Junit test that recreates the error and fixed FilterParser to default to using a MatchAllDocsFilter if the requested filter clause is left empty.
Also added fix and test for the Filters (with an "s") aggregation.

Closes #8438
[TEST] Delete index in test to release file handles
[BLOOM] Fix Bloom filter ram usage calculation

BloomFilter actually returned the size of the bitset as the
size in bytes so off by factor 8 plus a constant :)

Closes #8564
Update DiskThresholdDecider javadoc

Since v1.3.0, and issue #6201, the default values in code and documentation have been updated to 85% and 90% for low and high watermarks. However, the related javadoc still contains the initial values : this commit fix this.
Aggregations: Fix geohash grid doc counts computation on multi-valued fields.

Close #8512
Fix wrong error messages in MultiMatchQueryParser.

Also fix a typo in the comment

Close #8597
Fix a typo in a javadoc comment in MapperService.

Close #8575
Docs: Added new elasticsearch-river-kafka plugin to the documentation (uses latest version of Kafka, EL Bulk API, and supports concurrent requests)

Closes #8518
Docs: Remove reference to imaginary "no_docs_query"

No reference to it in the source code except this file.

Closes #8566
Fix error in documentation

Indexation does not fail if no timestamp provided when there is a default value defined in mapping.
Missing quote in the example
Docs: Update update-settings.asciidoc

Inconsistent indentation

Closes #8525
Docs: Update plugins.asciidoc on river plugins section

Adding links to Amazon S3 and Google Drive river plugins

Closes #8544
Docs: Reword note regarding _source for accuracy

Previously it suggested _source was always present, when that is not the case.

Closes #8491
Expose dist/pre/post options for SpanNotQuery
Use static int for easier to read code
Cleaner error handling. Pre without post (or vice versa) is not an error condition. Set appropriate defaults for pre/post.