Fixed highlighting inconsistencies between REST and Java api

Exposed HighlightBuilder missing global options in Java API: fragmentSize, numOfFragments, highlightFilter, boundaryMaxScan and boundaryChars
Exposed SearchRequestBuilder missing global options shortcuts: setHighlighterFragmentSize, setHighlighterNumOfFragments, setHighlighterFilter, setHighlighterBoundaryMaxScan, setHighlighterBoundaryChars, setHighlighterFragmenter, setHighlighterPhraseLimit & setHighlighterForceSource

Closes #5281
[TEST] Wait for shards to allocate before cleaning caches
Update has-parent-filter.asciidoc

"This filter return child..." => This filter returns child...
An improvement to unicast discovery to also ping nodes the node itself received a ping from.
Also moved the unicast tests all in a single package.

Closes #5508
[TEST] decreased number of replicas to 0 in refresh tests

Some tests disable refresh and verify that documents cannot be found without an explicit refresh. With at least one replica and waiting for yellow though, it can happen that we start indexing docs when the replicas are not ready yet, and as soon as they become ready they get refreshed, causing the newly added docs to be unexpectedly found. Solution is to disable replicas for these specific tests.
Search template: Fix support for source parameter

If a search template was created using the source parameter, the
content of the parameter was put as source instead of sourceTemplate

Fixes #5556