selftests: Enhance kselftest_harness.h to print which assert failed

selftests: Enhance kselftest_harness.h to print which assert failed

When a test process is not able to write to TH_LOG_STREAM, this step
mechanism enable to print the assert number which triggered the failure.
This can be enabled by setting _metadata->no_print to true at the
beginning of the test sequence.

Update the seccomp-bpf test to return 0 if a test succeeded.

This feature is needed for the Landlock tests.

Signed-off-by: Mickaël Salaün <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: Shuah Khan <[email protected]>
Cc: Will Drewry <[email protected]>
Link: https://lkml.kernel.org/r/CAGXu5j+D-FP8Kt9unNOqKrQJP4DYTpmgkJxWykZyrYiVPz3Y3Q@mail.gmail.com
Signed-off-by: Shuah Khan <[email protected]>