LU-12027 utils: fix "lfs find -amctime" comparison

LU-12027 utils: fix "lfs find -amctime" comparison

For matches that are "equal" to the specified time, they must match
within the smallest unit specified.  For example, "-mtime 24h" would
match anything within 1h of 24h ago, similar to how "-size 100M" will
match anything within 1MB of 100MB.

Test-Parameters: trivial fstype=zfs
Fixes: 355c8a529a3a ("LU-12027 utils: add units to 'lfs find -amctime'")
Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: Ib1eb4e626b712bb75f13b075849f959f203ebbe5
Reviewed-on: https://review.whamcloud.com/34658
Tested-by: Jenkins
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Wang Shilong <wshilong@ddn.com>
Reviewed-by: Jian Yu <yujian@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>