Provide a base plugin for indexing swift

Summary
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We want to be able to search swift objects and containers based on their structured and unstructured metadata.

Motivation
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Swift does not provide a structured search capability today and does not provide complex querying such as date ranges, geo spatial location, etc on that metadata. Many applications can be enabled with a better metadata search.

Description
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IBM softlayer had a presentation on their initial usage of swift and some application capabilities that are possible with an ElasticSearch integration at the Mitaka design summit.

They performed an initial integration as a standalone project that is similar to searchlight concepts and needs to be resolved with searchlight architecture. Their initial presentation is here:

https://www.openstack.org/summit/tokyo-2015/videos/presentation/boosting-the-power-of-swift-using-metadata-search

Here are some keypoints from the Mitaka prioritization meeting:

 * Swift had pain points with creating a query abstraction layer
 * Notifications need to be resolved
 ** Last summit, Swift group preferred Zaqar, but not sure if set in stone. Doubts about the general model and performance at scale (would have to support minimum of 5k-20k notifications/sec without flinching)
 ** SoftLayer uses RabbitMQ, will likely continue to...considering Kafka as well
 ** Search API part of swift? Possibly redirect to SL, still allows custom middleware in swift to handle specific customer cases but translates to searchlight

 * Searchlight needs configurable dynamic template mappings?
 ** Would be very helpful - lack of better mappings and/or templates was pain point for SoftLayer

https://etherpad.openstack.org/p/searchlight-swift-workpad

https://etherpad.openstack.org/p/mitaka-openstackux-swift

Testing
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Brief instruction for reviewers to exercise the changes, including expected results where non-obvious.

Outside Dependencies
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Is this functionality already supported in other services? List the appropriate API calls and if they are extensions or base API functionality.

This should describe any cross project dependencies. This should include:
  * changes to OpenStack services
  * changes to OpenStack services clients (python-*client)
  * changes in external projects
Links to particular patches should be included in the whiteboard area.

Requirements Update Required
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