Merge pull request redis#580 from go-redis/fix/flush-db-async

Add FlushDBAsync and FlushAllAsync

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Merge pull request redis#573 from go-redis/fix/no-error-on-empty-pipe…

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Don't return an error when pipeline is empty

Merge pull request redis#571 from go-redis/fix/on-connect

Fix/on connect

Cleanup tests

Merge branch 'master' of github.com:go-redis/redis

Merge branch 'master' of github.com:go-redis/redis

Merge branch 'master' of github.com:go-redis/redis

Merge branch 'master' of github.com:go-redis/redis

Merge pull request redis#552 from paulzhol/master

Fix typo in ClusterClient.TxPipelined()