LU-16977 utils: access_log_reader accesses beyond batch array

LU-16977 utils: access_log_reader accesses beyond batch array

Fixed access_log_reader accesses sorted batch array beyond upper
boundary when batch-fraction 100%: consider fraction = 100% as a
special case, which requires no sorting and filtering.
Use a separate thread function to process 100% fraction case.
Made some minor changes using enum type to nicefy the code.

Test-Parameters: trivial testlist=sanity
Signed-off-by: Alexandre Ioffe <aioffe@ddn.com>
Change-Id: Iba1734b17dc901875f343c793688aec17b9f7a93
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/51754
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Timothy Day <timday@amazon.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>