* master: (911 commits)
  [TEST] wait for yellow after setup doc tests (elastic#18726)
  Fix recovery throttling to properly handle relocating non-primary shards (elastic#18701)
  Fix merge stats rendering in RestIndicesAction (elastic#18720)
  [TEST] mute RandomAllocationDeciderTests.testRandomDecisions
  Reworked docs for index-shrink API (elastic#18705)
  Improve painless compile-time exceptions
  Adds UUIDs to snapshots
  Add test rethrottle test case for delete-by-query
  Do not start scheduled pings until transport start
  Adressing review comments
  Only filter intial recovery (post API) when shrinking an index (elastic#18661)
  Add tests to check that toQuery() doesn't return null
  Removing handling of null lucene query where we catch this at parse time
  Handle empty query bodies at parse time and remove EmptyQueryBuilder
  Mute failing assertions in IndexWithShadowReplicasIT until fix
  Remove allow running as root
  Add upgrade-not-supported warning to alpha release notes
  remove unrecognized javadoc tag from matrix aggregation module
  set ValuesSourceConfig fields as private
  Adding MultiValuesSource support classes and documentation to matrix stats agg module
  ...

* master: (184 commits)
  Add back pending deletes (#18698)
  refactor matrix agg documentation from modules to main agg section
  Implement ctx.op = "delete" on _update_by_query and _reindex
  Close SearchContext if query rewrite failed
  Wrap lines at 140 characters (:qa projects)
  Remove log file
  painless: Add support for the new Java 9 MethodHandles#arrayLength() factory (see https://bugs.openjdk.java.net/browse/JDK-8156915)
  More complete exception message in settings tests
  Use java from path if JAVA_HOME is not set
  Fix uncaught checked exception in AzureTestUtils
  [TEST] wait for yellow after setup doc tests (#18726)
  Fix recovery throttling to properly handle relocating non-primary shards (#18701)
  Fix merge stats rendering in RestIndicesAction (#18720)
  [TEST] mute RandomAllocationDeciderTests.testRandomDecisions
  Reworked docs for index-shrink API (#18705)
  Improve painless compile-time exceptions
  Adds UUIDs to snapshots
  Add test rethrottle test case for delete-by-query
  Do not start scheduled pings until transport start
  Adressing review comments
  ...