selftests/bpf: Add bloom map success test for userspace calls

This patch has two changes:
1) Adds a new function "test_success_cases" to test
successfully creating + adding + looking up a value
in a bloom filter map from the userspace side.

2) Use bpf_create_map instead of bpf_create_map_xattr in
the "test_fail_cases" and test_inner_map to make the
code look cleaner.

Signed-off-by: Joanne Koong <joannekoong@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20211029224909.1721024-4-joannekoong@fb.com