Suffix

After this patch, A_min set minimum for A, A_max set maximum for A,
A_fixed set fixed value for A, which means will not covered by setting after it.

This feature is useful when we set a parameter and do not want it covered by
new value late.

We need it when running case in loops.

There's a func ```normalize_data_size``` in ````virttest/utils_misc.py```, maybe which can meet your needs