Add `shard_min_doc_count` parameter for significant terms similar to `shard_size`

Significant terms internally maintain a priority queue per shard with a size potentially
lower than the number of terms. This queue uses the score as criterion to determine if
a bucket is kept or not. If many terms with low subsetDF score very high
but the `min_doc_count` is set high, this might result in no terms being
returned because the pq is filled with low frequent terms which are all sorted
out in the end.

This can be avoided by increasing the `shard_size` parameter to a higher value.
However, it is not immediately clear to which value this parameter must be set
because we can not know how many terms with low frequency are scored higher that
the high frequent terms that we are actually interested in.

On the other hand, if there is no routing of docs to shards involved, we can maybe
assume that the documents of classes and also the terms therein are distributed evenly
across shards. In that case it might be easier to not add documents to the pq that have
subsetDF <= `shard_min_doc_count` which can be set to something like
`min_doc_count`/number of shards  because we would assume that even when summing up
the subsetDF across shards `min_doc_count` will not be reached.

closes #5998
closes #6041
Node version sometimes empty in _cat/nodes
closes #5480
[DOCS] Update nodes documentation with all headers

Adds a table with the exhaustive list of all available headers with a brief description (mostly from `org.elasticsearch.rest.action.cat.RestNodesAction`) so that people do not need to go searching for them in the code like I did, or search through `nodes?help`.
Changed the respnose structure of the percentiles aggregation where now all the percentiles are placed under a `values` object (or `values` array in case the `keyed` flag is set to `false`

Closes #5870
clarify that CMS defaults change is coming in 1.2
Fix _cat/allocation rest test

The rest test for _cat/allocation was failing due to a regular
expression not accounting for space-padded right-justified text.

Also added Improvements to regular expressions to be smarter about optional values
and to use '+' instead of '*' where applicable.
Fix stack overflow in _cat/recovery test.

This fixes a stack overflow in the test for the _cat/recovery API.
The regular expression that tests the response body was modified to
handle large responses properly.
Integration tests for benchmark API.

- Randomized integration tests for the benchmark API.
- Negative tests for cases where the cluster cannot run benchmarks.
- Return 404 on missing benchmark name.
- Allow to specify 'types' as an array in the JSON syntax when describing a benchmark competition.
- Don't record slowest for single-request competitions.

Closes #6003, #5906, #5903, #5904
it's safe to use OneMerge.getTotalBytesSize (fixed in LUCENE-4775)
Fix for benchmark test

- Fix bug where repeatedly calling computeSummaryStatistics() could
  accumulate some values incorrectly.
- Fix check for number of responsive nodes on list is <= number of
  candidate benchmark nodes.
- Add public getters for summary statistics
- Add javadoc for new getters
- Add javadoc comments about API use
The percolator needs to deleted percolator documents into account when running in near realtime mode.

This bug only occurs in non-realtime mode when query, filter, facet or aggs is used.

Closes #5843
Closes #5840
Added FilteredQuery to the list of forbidden apis
A number of changes to fix reduce failures if shard failures have occurred:
* The shardTopDocs array should get created with the size equal to the total number of shard level requests and not the total number of requests that have a shard level result.
* Make sure no null TopDocs entires are passed down to TopDocs#merge
* Added dedicated scroll tests that tests scrolling on an index that has missing shards due to node failure.
* Made sure that the sort fields in SimpleNestedTests exists by adding the fields in the mapping during index creation.

Closes #6022
Update fielddata.asciidoc

Fixed default value for circuit breaker
Update fielddata.asciidoc

Spelling correction
Temporarily disabling benchmark tests.

Relates #6094
[TEST] Fixed pathological regex in cat.recovery

Fixes #6070
[TEST] cat.recovery with replicas can have 100.0%
[DOCS] fixed typo in multi term vectors docs
[DOCS] fixed broken json in multi term vectors docs