tests: check for the kernel taint after each test

This will allow to catch the first oops or warning. And this is notably useful for checking if the reallocation of the kernel collection stack is correct.

However, once a kernel is tainted, we can't reset the flag short of rebooting the kernel. So this means we can only catch the first kernel warning.

Note: enable KASAN to have a reliable detection of failure in the previously mentioned test.