[TESTS] Fix incorrect discovery options.
[DOCS] Added spring data elasticsearch integration
[DOCS] Various aggregation doc fixes
For unicast zen discovery don't overwrite a ping response for a node if the previous ping response has a set master and the current response hasn't.

Per single main ping request we maintain the received ping response per node. Each node level ping response is mapped into that. If from a previous node level ping request the response has already been set for a node, it will be overwritten. We give higher value to the latest response. This change makes sure that this doesn't happen if the previous response has a set master and the current response hasn't a set master. Otherwise a node will lose the fact that another node has elected itself as master, the result of that would be that there would multiple master nodes in a single cluster.

Closes #5413
[TESTS] Added AwaitsFix
Invoke postCollection on aggregation collectors.
Also cleanup how facet and aggs collector are used inside the QueryCollector

Closes #5387
ContextSuggester
================

This commit extends the `CompletionSuggester` by context
informations. In example such a context informations can
be a simple string representing a category reducing the
suggestions in order to this category.

Three base implementations of these context informations
have been setup in this commit.

- a Category Context
- a Geo Context

All the mapping for these context informations are
specified within a context field in the completion
field that should use this kind of information.