lib/event: fix and unify error message

Signed-off-by: Ruoyu <liangry@ucweb.com>
Signed-off-by: Hitoshi Mitake <mitake.hitoshi@lab.ntt.co.jp>
sheep/request: fix potential incorrect cluster info refcnt

For fear that req->data is not allocated successfully, move
increament of client info refcnt after memory alloc is reasonable.

Signed-off-by: Ruoyu <liangry@ucweb.com>
Signed-off-by: Hitoshi Mitake <mitake.hitoshi@lab.ntt.co.jp>