Cluster: fix logic to detect we are among a minority.
Cluster: fix logic to detect we are among a minority.

In the cluster evaluation function we are supposed to set the cluster
state as "fail" if we are among a minority, however the code was not
detecting to be into a minority partition if exactly half the masters
were reachable, which is a minority.

JackieXie168/redis,JackieXie168/redis,JackieXie168/redis,JackieXie168/redis