v2.5.0-beta1

curvefs/client: bug fix about memcache

1. When running the vdbech task, the memory usage of the mount point is very high
2. When running the vdbech task, the mount will coredump or the task will have data inconsistency
3. The memcache server fails over and then restarts and cannot be used by the client anymore

Signed-off-by: ilixiaocui <ilixiaocui@163.com>