redis script command support

[lukemakeit]

Problem

redis script command not support.

Solution

Send the script command to all Redis servers for execution, and get one of the results and return it to the user client.

Result

> script load "return redis.call('hset',KEYS[1],KEYS[1],KEYS[1])"
"dbbae75a09f1390aaf069fb60e951ec23cab7a15"
> script exists dbbae75a09f1390aaf069fb60e951ec23cab7a15
1) (integer) 1

[w4096]

Add a member named server_index in struct msg. If the value is >=0, use msg->server_index as target server index. In this way, we don't need redis_script_idx and scan_server_idx at all.

[w4096]

If we can implement a function redis_fragment_broadcast which can broadcast a request to all servers, we can implement broadcast commands like DBSIZE, FLUSHALL easily. What I mean is this function is not general enough, which can only handle SCRIPT command.