CLUSTER SLOTS: don't output failing slaves.
CLUSTER SLOTS: don't output failing slaves.

While we have to output failing masters in order to provide an accurate
map (that may be the one of a Redis Cluster in down state because not
all slots are served by a working master), to provide slaves in FAIL
state is not a good idea since those are not necesarely needed, and the
client will likely incur into a latency penalty trying to connect with a
slave which is down.

Note that this means that CLUSTER SLOTS does not provide a *complete*
map of slaves, however this would not be of any help since slaves may be
added later, and a client that needs to scale reads and requires to
stay updated with the list of slaves, need to do a refresh of the map
from time to time, anyway.

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