Handle multidigit file size for log rolling

Set the logshifter filesize to any value greater than 10, it will read
only the unit's digit.

Eg, set the LOGSHIFTER_PHP_MAX_FILESIZE=15M, when the php.log reach 5M,
it will rotate the log.
https://bugzilla.redhat.com/show_bug.cgi?id=1078765