selftests/livepatch: wait for atomic replace to occur

On some machines with a large number of CPUs there is a sizable delay
between an atomic replace occurring and when sysfs updates accordingly.
This fix uses 'loop_until' to wait for the atomic replace to unload all
previous livepatches.

Reported-by: CKI Project <cki-project@redhat.com>
Closes: https://datawarehouse.cki-project.org/kcidb/tests/redhat:1413102084-x86_64-kernel_upt_28


Signed-off-by: Ryan Sullivan <rysulliv@redhat.com>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Acked-by: Joe Lawrence <joe.lawrence@redhat.com>
Link: https://lore.kernel.org/r/20240822173122.14760-1-rysulliv@redhat.com


Signed-off-by: Petr Mladek <pmladek@suse.com>