Cluster: some bias towwards FAIL/PFAIL nodes in gossip sections.
Cluster: some bias towwards FAIL/PFAIL nodes in gossip sections.

This improves PFAIL -> FAIL switch. Too late at this point in the RC
releases to add proper PFAIL/FAIL separate dictionary to do this in a
less randomized way. Tested in practice with experiments that this
helps. PFAIL -> FAIL average with 20 nodes and node-timeout set to 5
seconds takes 2.5 seconds without this commit, 1 second with this
commit.

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