databases/elasticsearch: Update to 6.2.4.

=== Bug fixes

Engine::
- Harden periodically check to avoid endless flush loop

Ingest::
- Don't allow referencing the pattern bank name in the pattern bank

Java High Level REST Client::
- Bulk processor#awaitClose to close scheduler

Java Low Level REST Client::
- REST client: hosts marked dead for the first time should not be
  immediately retried

Network::
- Cross-cluster search and default connections can get crossed

Percolator::
- Fixed bug when non percolator docs end up in the search hits
- Fixed a msm accounting error that can occur during analyzing a
  percolator query
- Fix more query extraction bugs.
- Fix some query extraction bugs.

Plugins::
- Plugins: Fix native controller confirmation for non-meta plugin

Search::
- Propagate ignore_unmapped to inner_hits

Settings::
- Archive unknown or invalid settings on updates

(fhajny)