The project is forked from: https://github.com/oliver006/redis_exporter

Modified it to support redis sentinel.

Add flags:

Name	Environment Variable Name	Description
sentinel.addrs	SENTINEL_ADDRS	Address of the Redis sentinels spilt by ',', defaults to localhost:26379.
redis.master	REDIS_MASTER	Redis master name the sentinels monitoring, defaults to mymaster.

And the flag redis.addr was ignored.

Add a label in metric redis_instance_info named "redis_master_addr" and the value is "<masterIp>:<masterPort>" that the sentinels monitoring

When every scrape request arrives, it will trying to find redis master address by sentinel.addrs and redis.master by command sentinel get-master-addr-by-name <masterName>, and then process as before with redis master address as redis.addr.