TODO: refuctor...
Returns 1 IPv4 address and port.
$ gsr --help
-redis
use redis to save result. (default false)
-redisl
use redis to load cache. (default false)
-socket-redis
use unix domain socket to connect with redis. (default false)
-srv string
string of SRV RR (default "_http._tcp.mxtoolbox.com")
-ttl int
TTL of redis-cache (default 20)
$ gsr -srv service.srv.local
xxx.xxx.xxx.xxx:80 # without linefeed.