Support for sleeping and retrying non-scroll searches after encountering a shard failure.
After brief discussion with Jeff, moved the retry and sleep params up t ES.__init__() to follow the same precedent as raise_on_bulk_item_failure.
Only make one non-scroll search attempt by default.
Merge pull request #1 from simonyun/no-failed-shards

Sleep-retry on shard failure for non-scroll searches