[DOCS] Fix wrong explanation in configuration.asciidoc

Replaced network.host with node.name to match config file
[DOCS] Added note about dely in clearing filter cache.

Closes #5231
NPE in PluginsService when starting elasticsearch with a wrong user

When starting elasticsearch with a wrong linux user, it could generate a `NullPointerException` when `PluginsService` tries to list available plugins in `./plugins` dir.

To reproduce:

* create a plugins directory with `rwx` rights for root user only
* launch elasticsearch from another account (elasticsearch for example)

It was supposed to be fixed with #4186, but sadly it's not :-(

Closes #5195.
Change GetFieldMapping API to broadcast requests to nodes hosting the relevant indices.

This is due to the fact that have to have mappers in order to return the response.

Closes #5177
[TEST] Added get field mapping test variant that tests with a cluster that has a master only node.
Added TransportGetFieldMappingsIndexAction that uses TransportSingleCustomOperationAction as base class, with the goal to reuse common logic (like: retry on failures, shard picking, connecting to nodes)
Need use ensureYellow() b/c get mapping request checks the mapping on the master node
Need use ensureYellow() b/c get mapping request checks on actual shard instead of master node
Made SearchContextHighlight.Field class immutable to prevent from erroneously updating it, as it doesn't necessarily map to a single field

A Field instance can map to multiple actual fields when using wildcard expressions. Each actual field should use the proper highlighter depending on the available data structure (e.g. term_vectors), while we currently select the highlighter for the first field and we keep using the same for all the fields that match the wildcard expression.

Modified also how the PercolateContext sets the forceSource option, in a global manner now rather than per field.

Closes #5175
Recycler: better lifecycle control for pooled instances (#5214)

- introduce additional destroy() callback that allows better control
over internals of recycled data
- introduced AbstractRecyclerC as superclass for Recycler factories
(Adrien) with empty destroy() by default
- added tests for destroy()
- cleaned up Recycler tests (reduce copy&paste)
Implement BlendedTermQuery#extractTerms to support highlighing.

some of the highlighters require term extraction to be implemented in
order to work. BlendedTermQuery doesn't implement the trivial extraction.

Closes #5246
Add coming 0.90.12 version to the constants
remove thread local recycler

the thread local recycler requires obtain and recycle to be called on the same thread, while other recyclers do not. Also, it can create heavy recycle usage since it depends on the threads that its being used on. The concurrent / pinned thread base one is by far better than the pure thread local (and is the default) one since it more easily bounds the elements recycled, while still allowing to mix obtain and recycle across threads.

We will end up using the paged recyclers more and more, for example, in our networking output buffer, where obtaining will happen on one thread, while recycling can potentially occur on another thread (the callback thread). Since the limit of binding to a thread of the 2 calls is not really needed, and our best implementation supports going cross threads, there is no real need to impose this restriction.
Remove nanoTime in global cluster randomization in favor of deriving the
seed from the main master seed. Removed shared cluster's seed entirely.

The problem here is that if you don't give cluster's seed then test times
fluctuate oddly, even for a fixed -Dtests.seed=... This shouldn't be the
case -- ideally, the test ran with the same master seed should reproduce
pretty much with the same execution time (and internal logic, obviously).

From the code point of view "global" variables are indeed a problem
because JUnit has no notion of before-suite hooks. And RandomizedRunner
doesn't support context accesses in static class initializers (this is
intentional because there is no way to determine when such initializers
will be executed). A workaround is to move such static global variables to
lazily-initialized methods and invoke them (once) in @BeforeClass hooks.