Merge branch 'master' into retention

Conflicts:
    graylog2-server/src/main/java/org/graylog2/indexer/Indexer.java
    graylog2-server/src/main/java/org/graylog2/indexer/indices/Indices.java

manually added changes from 28cdde981ce96892882158b7848eb2c792648fb0 to Indexer.java to EsNodeProvider.java