logger: remove extra spaces after timestamp
logger: remove extra spaces after timestamp

Rename all the timestamp functions to make it clear they supply that extra
space themselves, move it to before the timestamp, and delete two printed spaces.
Message-Id: <8e84920e8eb04ed7236d4e9ba66dd7204dd63a5d@scylladb.com>

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