stress-ng tests not handling timeout exit codes completely

[Jeff Lane ]

stress-ng tests use timeout to forcefully clean up should one of the stressors hang. This results in an exit of either 124 or 137, depending on whether SIGKILL was necessary to halt a process.

Currently, memory_stress-ng only catches 137, but there have been cases where 124 occurs too.

Need to modify memory-stress-ng to catch both errors.

Also need to review other scripts that call stress-ng (disk and cpu stress) to ensure they too catch both exit codes.