Better address udpate strategy when processing gossip sections.
Better address udpate strategy when processing gossip sections.

The change covers the case where:

1. There is a node we can't reach (in fail or pfail state).
2. We see a different address for this node, in the gossip section sent
to us by a node that, instead, is able to talk with the node we cannot
talk to.

In this case it's a good bet to switch to the address reported by this
node, since there was an address switch and it is able to talk with the
node and we are not.

However previosuly this was done in a dangerous way, by initiating an
handshake. The handshake, using the MEET packet, forces the receiver to
join our cluster, and this is not a good idea. If the node in question
really just switched address, but is the same node, it already knows about
us, so we just need to perform an address update and a reconnection.

So with this commit instead we just update the address of the node,
release the node link if any, and attempt to reconnect in the next
clusterCron() cycle.

The commit also improves debugging messages printed by Cluster during
address or ID switches.

maodeyi/redis_lua,louisliangjun/redis,louisliangjun/redis,splitice/redis,maodeyi/redis_lua,ramonsnir/redis,splitice/redis,louisliangjun/redis,louisliangjun/redis,ramonsnir/redis,splitice/redis,maodeyi/redis_lua,ramonsnir/redis,splitice/redis