Cluster test: use 20 instances.
Cluster test: use 20 instances.

This makes tests a bit slower, but it is better to test things at a
decent scale instead of using just a few nodes, and for a few tests we
actually need so many nodes.

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