Lower HISTORY limit to 25 for scripts to create multiple directories

This patch lowers HISTORY value limit from 28 to 25. When HISTORY value
is greater than 25 then sa1 script creates a month-by-month directory
structure in /var/log/sa to save datafiles.
This value guarantees that we will always have a full history and that
no files will be overwritten unintentionally.

Signed-off-by: Sebastien GODARD <sysstat@users.noreply.github.com>