tests: validate CONFIG_HZ_1000

tests: validate CONFIG_HZ_1000

If we plan to use dm throttling for mirror targets - we actually
have to check whether kernel runs with CONFIG_HZ_1000 - if it does
not the whole idea of throttling is actually not working in the
testsuite as within a single 'tick' with HZ 100 way too much date
is being moved on any modern hardware - and since there is no plan
to change this in kernel - we simply avoid using throttling on such
kernel and test needs to work differently - either ignore results
or use much larger mirror sizes...