Add switch to stop memtest when error was detected.

[the4anoni]

[galkinvv]

Thanks for suggestion, good idea. I have some plans on adding timed mode testing (exit infinite testing after some specified time) - that mode will immediately exit on error.

The current default behaviour "continuing after 1st error" is useful in 2 scenarious:

• interactive managing of frequencies in parallel with memtest_vulkan run
• analyzing the errors counts/patterns/conditions.