[DOCS] Completion suggest: Clarify de-duplication, optimize/merge

This contribution is based on the feedback given in issue #4254 and
issue #4255, and should clear things up, when suggestions are being
removed and not displayed anymore after deletion of data.
Added a FsStats.total section that sums up all stats for the different path.dirs. Added `disk_io_size` and `disk_io_op` to the toXContent output, summing up `disk_read_size+disk_write_size` and `disk_writes+disk_reads` respectively.

Closes #4344 , Closes #4343
remove help command, list all cat commands in /_cat?h endpoint
Cat: Add nodes column descriptions.
Cat: Add descs for rest of actions.
Fix _all boosting.

_all boosting used to rely on the fact that the TokenStream doesn't eagerly
consume the input java.io.Reader. This fixes the issue by using binary search
in order to find the right boost given a token's start offset.

Close #4315
[DOCS] Fix outdated link to wonderdog in community integration
[Docs] Document which encoding should be used in order to make sense of the offsets returned by the term vectors API.

Close #4363
Apply slop correctly if phrase query is wrapped in a filtered query.

If a phrase query is wrapped in a filtered query due to type filtering
slop was not applied correctly. Also if the default field required a
type filter the filter was not applied.

Closes #4356
Optimize dynamic mapping updates on master by processing latest one per index/node
Instead of processing all the bulk of update mappings we have per index/node, we can only update the last ordered one out of those (cause they are incremented on the node/index level). This will improve the processing time of an index that have large updates of mappings.
closes #4373
update the test to use the same API as 0.90
so backports will be simpler for now
Fixed local option explanation in TESTING readme
Add an `usage` key to the CPU section of OsStats.toXContent.

 This is just the sum of existing `sys` and `user`

Closes #4374
Update percolator highlighting docs.
Query String caching could cause matched_filters not working

When searching with a query containing query_strings inside a bool query, the specified _name is randomly missing from the results due to caching.

Closes #4361.
Closes #4371.
- fixing update mapping tests for index operations so the number of request will be based on the index thread pool size
- added update mapping tests for bulk operations
add node and order to the source of update mapping
Add generic assertion to all aggs.bucket tests to check if all shards were successful
Move Thread.sleep test to awaitBusy
Added refCount assertion due to LUCENE-5362