[TEST] made catch request more accurate in REST tests runner

Excluded 404, 403 and 409 status codes from the catch request as they have their own specific catch codes
[TESTS] Fix MinDocCountTests.

The new include/exclude support for global ordinals didn't exclude terms in
`buildAggregation` (which is required if minDocCount is 0).
[TEST] cat.recovery regex still causing occasional JVM regex stackoverflows.
Try making the capture possessive to prevent recursion
Allow to change concurrent merge scheduling setting dynamically
Allow to change the concurrent merge scheduler settings dynamically using the update settings API
closes #6098
[TESTS] Improve BenchmarkIntegrationTest's check that percentiles are increasing.

Percentiles are supposed to be monotonically increasing but floating-point
rounding issues can come into play and make the test fail if checks are too
strict.
Check if root mapping is actually valid

When a mapping is declared and the type is known from the uri
then the type can be skipped in the body (see #4483). However,
there was no check if the given keys actually make a valid mapping.

closes #5864
closes #6093
add failing test for shard_min_doc_count
refactor: unify terms and significant_terms parsing

Both need the requiredSize, shardSize, minDocCount and shardMinDocCount.
Parsing should not be duplicated.
refactor: make requiredSize, shardSize, minDocCount and shardMinDocCount a single parameter

every class using these parameters has their own member where these four
are stored. This clutters the code. Because they mostly needed together
it might make sense to group them.
I hope that this makes the code more readable and also that if avoids
errors such as mixing up the int/long parameters in the future.
use shard_min_doc_count also in TermsAggregation

This was discussed in issue #6041 and #5998 .
add documentation of `shard_min_doc_count`