Fix reading multiple blktrace replay files

Fix reading multiple blktrace replay files

During fio replay, the input file would be checked first by is_blktrace()
if it is a blktrace output file. If so, however, this would treat the
read_iolog option as one single file and ignore multiple files seperated by ":"

This commit contains the fixation that read input file name by index
before doing the check

Signed-off-by: luye <luye.yelu@bytedance.com>