JVMCBC-9: After failover, select different node.

Also, this change hardens the handler when ops are cancelled so that anything that will
be thrown by the subscriber does not kill the event loop as well.

Change-Id: I8fcb3fabe060f5410f32fa5761c5e2e239ee52a6
Reviewed-on: http://review.couchbase.org/41472
Reviewed-by: Michael Nitschinger <michael.nitschinger@couchbase.com>
Tested-by: Michael Nitschinger <michael.nitschinger@couchbase.com>