Fix: compatibility with elasticsearch 2

[ysbaddaden]

Fixes a number of deprecated features in elasticsearch 1 that got removed in elasticsearch 2:

• Replaces multi-field type for a string with a nested field (deprecated in elasticsearch 1).
• Avoids the . in field definitions (invalid in elasticsearch 2).
• Removes the path definition that isn't needed (deprecated in elasticsearch 2).
• Renames default_index as default (deprecated in elasticsearch 1).
• Use size instead of limit filter (deprecated in elasticsearch 1).
• Uses aggregations instead of facet searches (deprecated in elasticsearch 2).

These changes are compatible with elasticsearch v1.7 and v2.4 and the elasticsearch migration plugin returns a full green status.

To test against elasticsearch 2, you must tweak the docker compose service. For some reason the index.max_result_window setting must be increased from the default of 10000. For example:

services:
  elasticsearch:
    image: elasticsearch:2.4-alpine
    command: elasticsearch -Dindex.max_result_window=1000000

[ysbaddaden]

Hum, it's not ready, I have a few issues after upgrading to elasticsearch 2. No issues no more.