Ping interval

[leibale]

fix #1598 fix #2276

add support for pingInterval

[jbeangreen]

@leibale pingInterval solves the primary subscriber client connection timeout tested with HAProxy but when connecting to Redis using both a Publisher and Subscriber it will fail as you cannot send commands on the subscriber client.

• [redis-subscriber] Error: Cannot send commands in PubSub mode

[leibale]

@jbeangreen nice catch! wanna open an issue about this?

[jbeangreen]

@leibale Sadly I'm swamped releasing a new stack, just wanted to bring this to your attention in case anyone else hits this issue. We have an advanced setup so I ended up jumping to ioredis as it allows to bypass the loadbalancer and connect to redis sentinels directly.