apps/iotune: print out which config file updated
apps/iotune: print out which config file updated

To make result message clearer, output written config file name when it
specified.

Fixes scylladb/scylla#3660

Signed-off-by: Takuya ASADA <4ebfb6f510af412d6e89fefa3ab96d9c8b5e3fff@scylladb.com>
Message-Id: <20180808034625.16583-1-4ebfb6f510af412d6e89fefa3ab96d9c8b5e3fff@scylladb.com>

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