Support backoff and retry when search fails because of server/network busy or error

Zhibin Mairequested to merge
augmenter_search_retry into master

Support backoff and retry when search fails because of server/network busy or error. The search (client) are only used by Augmenter indexing and re-indexing a given list of records (record ids). The queries are well-constructed programmatically.

Edited by Zhibin Mai

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