Enhancement: Add tmt check for kmemleak

[sbertramrh]

We are attempting to automate testing on a debug kernel and want to incorporate triggering a kmemleak scan at the end of each test. If there is memleak detected then save the trace cat /sys/kernel/debug/kmemlek > $TMT_PLAN_DATA/some_file.log or any location tmt decides is best.

After reading about tmt.check functions I thought this would be a great next step.

So for each test, as with dmesg, we clear at the start: echo clear > /sys/kernel/debug/kmemleak

Scan at the end: echo scan > /sys/kernel/debug/kmemleak (should happen before capturing dmesg)

Capture contents of kmemleak as mentioned above. This file maybe empty.

See https://www.kernel.org/doc/html/latest/dev-tools/kmemleak.html

It is essential we get this process automated and this tmt module seems like the right fit for it.

cc: @thrix