io_tester: Truncate file right at once
io_tester: Truncate file right at once

After the file is created the testing workload is doomed to
use append-challenged-file. Also creating a file most likely
works in append-mode, which is also not very nice.

Truncate the file right at once for efficiency.

Signed-off-by: Pavel Emelyanov <c9a32589e048e044184536f7ac71ef92fe82df3e@scylladb.com>

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