Log Message:
Update databases/elasticsearch to 5.3.1

=== Breaking changes

Settings::
- Remove support for default settings

=== Enhancements

Core::
- Detect remnants of path.data/default.path.data bug

Network::
- Adjust default Netty receive predictor size to 64k

REST::
- Cluster stats should not render empty http/transport types

=== Bug fixes

Aggregations::
- The `filter` and `significant_terms` aggregations should parse the
  `filter` as a filter, not a query.
- Restore support for the `include/pattern` syntax.

Bulk::
- Reject empty IDs

Core::
- Improve performance of extracting warning value
- Restrict build info loading to ES jar, not any jar

Discovery::
- ZenDiscovery - only validate min_master_nodes values if local node
  is master

Index APIs::
- Honor update request timeout

Inner Hits::
- Replace `NestedChildrenQuery` with `ParentChildrenBlockJoinQuery`

Internal::
- Add infrastructure to mark contexts as system contexts

Java REST Client::
- Make buffer limit configurable in HeapBufferedConsumerFactory

Mapping::
- Preserve response headers when creating an index
- Fix NPE with scaled floats stats when field is not indexed

Network::
- Fix possible hang in local transport when nodes get concurrently
  disconnected

Plugin Repository Azure::
- Azure blob store's readBlob() method first checks if the blob exists

Reindex API::
- Fix reindex with a remote source on a version before 2.0.0

Search::
- Disable graph analysis at query time for shingle and cjk filters
  producing tokens of different size
- Fix cross-cluster remote node gateway attributes
- Use a fixed seed for computing term hashCode in TermsSliceQuery

Settings::
- Do not set path.data in environment if not set
- Correct handling of default and array settings

Stats::
- Handle existence of cgroup version 2 hierarchy

=== Upgrades

Internal::
- upgrade to Lucene 6.4.2