supernode增加存储驱动(storage driver)

[nonly]

背景

• 当前版本的supernode是将元信息存储在本地内存中；规模比较大时本地内存占用可能过多。

想法

• 希望增加一些常用存储的storage driver，例如redis等；用户可以根据需求选择不同的driver存储元信息；
• 目标是：可配置，可插拔，支持多种driver

[zhouhaibing089]

Looks very straightforward to replace all the ConcurrentHashMap with an interface.

[allencloud]

First of all, thanks sincerely for constantly using and supporting Dragonfly. We will try our best to keep Dragonfly better, and keep community and eco-system growing.

To get more feedback of Dragonfly's adoption in industry, would you mind helping comment in issue #219 to give more information about your enterprise's Dragonfly usage. Thanks a lot in advance. @nonly

[nonly]

@allencloud OK, I have commented.

[starnop]

Has been implemented. So close it now.