Cluster: error out quicker if port is unusable
Cluster: error out quicker if port is unusable

The default cluster control port is 10,000 ports higher than
the base Redis port.  If Redis is started on a too-high port,
Cluster can't start and everything will exit later anyway.

maodeyi/redis_lua,ramonsnir/redis,ttuna/msot-redis,ramonsnir/redis,slfs007/mk-redis,jxwr/redis,ksarch-saas/redis,MSOpenTech/redis,ksarch-saas/redis,HunanTV/redis,Hailei/redis,louisliangjun/redis,darksideofthemoo/redis-histogram,jxwr/redis,HunanTV/redis,himoca/redis,splitice/redis,darksideofthemoo/redis-histogram,MSOpenTech/redis,ttuna/msot-redis,ramonsnir/redis,HunanTV/redis,xuzhezhaozhao/redis_reading,himoca/redis,maodeyi/redis_lua,MSOpenTech/redis,MSOpenTech/redis,spearhead-ea/redis,splitice/redis,ttuna/msot-redis,ksarch-saas/redis,slfs007/mk-redis,splitice/redis,ttuna/msot-redis,himoca/redis,darksideofthemoo/redis-histogram,Hailei/redis,jxwr/redis,xuzhezhaozhao/redis_reading,darksideofthemoo/redis-histogram,spearhead-ea/redis,ttuna/msot-redis,slfs007/mk-redis,splitice/redis,maodeyi/redis_lua,xuzhezhaozhao/redis_reading,spearhead-ea/redis,Hailei/redis,MSOpenTech/redis,HunanTV/redis,Hailei/redis,louisliangjun/redis,ksarch-saas/redis,louisliangjun/redis,louisliangjun/redis,xuzhezhaozhao/redis_reading