Add more details when auto-failover happens

There are many possible causes of node auto-failover, for example,

• Hardware failures. E.g. Node, network or power failure.
• Unreliable communication among the nodes. E.g. Network congestion
• memcached slowdown or crash
• Out Of Memory problems.
• Time forward jump – unstable system clock.
• Machine freeze or process scheduling issues.
• Stability problems in a virtualized environment. E.g. unhealthy VMs due to overcommitted CPU, RAM.

Please enhance the messaging (UI and logs/Log tab) when a node is auto-failovered to indicate which of these issues is responsible. For example, you could indicate whether the missed heartbeat or not-ready bucket caused the failover.