[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
5882: put back Elasticsearch's 1.1 defaults for ConcurrentMergeScheduler
#6120 Remove SerialMergeScheduler (master only)

It's dangerous to expose SerialMergeScheduler as an option: since it only allows one merge at a time, it can easily cause merging to fall behind.

Closes #6120
#5882: fix docs
#6081: set IO throttling back to 20 MB/sec now that #6018 is fixed
Change key to keyed
fixed MetaData#concreteIndices to throw exception with a single index argument in case allowNoIndices == false and ignoreUnavailable == true

Closes #6137
improved IndicesOptions javadocs
Fix for benchmark test timeout

Lower number of random requests generated for each test so as not to
timeout on heavy tests.

Addresses #6094
Fix for hanging aborted snapshot during node shutdown

If a node is shutdown while a snapshot that runs on this node is aborted, it might cause the snapshot process to hang.

Closes #5958
[DOCS] Added "Aggregation" to all aggs titles
Log script change/add and removal at INFO level

Closes #6104
Significant_terms agg: added option for a background_filter to define background context for analysis of term frequencies

Closes #5944
[DOCS] Fix typos in context suggest
Use t-digest as a dependency.

Our improvements to t-digest have been pushed upstream and t-digest also got
some additional nice improvements around memory usage and speedups of quantile
estimation. So it makes sense to use it as a dependency now.

This also allows to remove the test dependency on Apache Mahout.

Close #6142