* Upgrade to Lucene 6.4.0
`ValueSource`s are now converted to `DoubleValueSource`s using the Lucene adapter made for the migration to the new API in 6.4.0.
Set lucene version to 6.4.0-snapshot-ec38570 and update all the sha1s/license
Fix invalid combo after upgrade in query_string query. split_on_whitespace=false is disallowed if auto_generate_phrase_queries=true
Adapt the expectations of some tests to the new format of the Lucene explain output
Since Lucene 6.2. the UkrainianMorfologikAnalyzer is available through the
lucene-analyzers-morfologik jar. This change exposes it to be used as an
elasticsearch plugin.