Sentinel test: restart_instance should refresh pid attrib.
Sentinel test: restart_instance should refresh pid attrib.

Also kill_instance was modified to warn when a test will try to kill the
same instance multiple times for error.

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