Add expiration for long time vacant scanners in Thrift2

In thrift1 implementation, the ThriftHBaseSerivceHandler holds a Cache with an expire time after access. This will make the long time vacant scanners be collected by gc. However, in thrift2 we do not have this feature and only use a map to store scanners and we need the client close the scanner manually. If not, the expired scanners will live in memory forever. In this case, I applied the cache expiration to thrift2 service.