Test: UpdateTests.stressUpdateDeleteConcurrency shouldn't turn off threaded operations

This may result in all network threads being busy for too long.
[HEALTH] Don't mark health as timed out if desired state is reached

Today we mark cluster health requests as timed out if the request has already
timed out. Yet, and implementation detail of the health request is that we are
waiting for events which can take quite some time if the machine is busy. If
we have already reached a valid state while waiting for events to be processed
we shouldn't mark the clusterstate as timed-out. This will help tests that
wait for green state with lots of nodes and shards to not fail the cluster health
calls.
[CLIENT] Only fetch the node info during node sampling

Today we are fetching a lot of information that is unneeded
for the sampling phase. We only really need the DiscoveryNode
to ensure the node is still there.
This commit clears all flags to be false on the NodeInfo call.
Test: predefine sort fields in mapping, otherwise during the test the field may not be found if it were to be introduced dynamically at index time.
[docs] explain default settings for parameters of decay functions

relates to #8624
[Docs] Fix missing new line
[Docs] fix consistency between examples
[TEST] Reduce possible number of indices in the test - 10 indices can create tons of shards
MLT Query: Fix exclude with artificial documents

Artificial documents get assigned a random id. When include is set to false
(default), the ids of these documents also get included, when they should
rather be ignored.

Closes #8679
[TEST] Use different index on each iteration to ensure less timeout prone tests
Test: add trace logging to RelocationTests

also improved error message when failing to delete a dummy doc
[TEST] Add an assert for null indices in InternalEngineIntegrationTest
[TEST] remove outdated TestLogging annotation

Conflicts:
	src/test/java/org/elasticsearch/bwcompat/UnicastBackwardsCompatibilityTest.java
	src/test/java/org/elasticsearch/recovery/RelocationTests.java
[TEST] move test to a different class that can disable publish timeout on demand
[TEST] add back accidetially removed test logging
[TEST] With pipelining disabled requests can come back in any order

Closes #8697
function_score: match only document with score above custom score threshold

functon_score matched each document regardless of the computed score.
This commit adds a query parameter `min_score` (-Float.MAX_VALUE default).
Documents that have a score lower than this threshold will not be mached.

closes #6952
Docs: Additional info about _score calculation

Description taken from http://www.elasticsearch.org/guide/en/elasticsearch/guide/current/multi-query-strings.html / 110_Multi_Field_Search/05_Multiple_query_strings.asciidoc

Closes #8635