selftests/bpf: Report program name on parse_test_spec error

Change test_loader.c:run_subtest() behavior to show BPF program name
when test spec for that program can't be parsed.

Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20230325025524.144043-2-eddyz87@gmail.com


Signed-off-by: Alexei Starovoitov <ast@kernel.org>