Some distros have huge rlimits and then the test takes forever, or
worse oom, or even worse, takse down the entire machine (which is
shouldn't be able to, but oh well, oom handling in linux).

Make sure we have a consistent rlimit by adjusting it manually.

v2: Use the default of 1024 from everywhere except ubuntu.

Cc: Tomi Sarvela <tomi.p.sarvela@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Arkadiusz Hiler <arkadiusz.hiler@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>