Fix sentinel connections

[garionphx]

When passing args to Redis(), using the connection_kwargs args allows us to use authentication and other connection features.

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Description of change

Modified the arguments passed to Redis() when forming Sentinel connections

[garry-t]

great, thank you!

[vladvildanov]

@garionphx Thanks for your contribution! Make sure that tests passes

[vladvildanov]

@garionphx Since this changes makes self.sentinel_kwargs argument completely redundant, it should be removed from constructor properties and it will be a breaking change.

[vladvildanov]

As this is the only place where self.sentinel_kwargs are used we have to remove it