MINOR: server: activate automatically check reuse for rhttp@ protocol

MINOR: server: activate automatically check reuse for rhttp@ protocol

Without check-reuse-pool, it is impossible to perform check on server
using @rhttp protocol. This is due to the inherent nature of the
protocol which does not implement an active connect method.

Thus, ensure that check-reuse-pool is always set when a reverse HTTP
server is declared. This reduces server configuration and should prevent
any omission. Note that it is still require to add "check" server
keyword so activate server checks.