semaphore: make semaphore's clock configurable
semaphore: make semaphore's clock configurable

Message-Id: <4129f38a63be125596da799361c3e497dee08e09@scylladb.com>

avikivity/seastar,syuu1228/seastar,cloudius-systems/seastar,dreamsxin/seastar,dreamsxin/seastar,scylladb/seastar,syuu1228/seastar,cloudius-systems/seastar,avikivity/seastar,cloudius-systems/seastar,scylladb/seastar,syuu1228/seastar,avikivity/seastar,scylladb/seastar,dreamsxin/seastar