[Core] Make sure redis sync context and async context connect to the same redis instance

[jjyao]

Why are these changes needed?

We are using ip for redis sync context connection but domain name for redis async context so there is a chance redis async context doesn't connect to the master.

I think what can happen is that during RedisContext::Connect(), the domain name is resolved to two ips (ip[0] is master, ip[1] is replica). sync context is connected to ip[0] so it's fine while async context is connected using domain name so it might be connected to ip[1] which is a replica. Later on we have check to make sure we are connected to the master but we only do the check for sync context so we don't realize that the async context is connected to the replica. Then when we use async context to send HGET request, replica will return MOVED (https://redis.io/commands/readonly/) to redirect us to the master and since we don't handle MOVED at that time, it failed.

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[vitsai]

oh nice