mem/ksm05: Add check for KSM sysfs existence.

Add check (the same as in ksm01) for the existence of KSM sysfs files.
Without it the testcase prints 665 lines of TBROK and then Segfaults on
systems without KSM support.

Signed-off-by: Cyril Hrubis <chrubis@suse.cz>