What varies accross machine is maria_pagecache_read_requests, but maria_pagecache_reads doesn't and
is the most interesting (helps verify that disk wasn't touched after preloading), that's all we keep.

mysql-test/r/maria-preload.result:
  unrepeatable variable removed
mysql-test/t/maria-preload.test:
  unrepeatable variable removed
storage/maria/ma_test_force_start.pl:
  portability fix for running under Windows