Currently we don't check data_file_directories existance before running iotune, therefore it's shows unclear error message. To make the message better, check the directory existance on scylla_io_setup. Fixes #3137 Signed-off-by: Takuya ASADA <syuu@scylladb.com> Message-Id: <1517200647-6347-1-git-send-email-syuu@scylladb.com>