selftests/bpf: revamp test_progs to allow more control

Refactor test_progs to allow better control on what's being run.
Also use argp to do argument parsing, so that it's easier to keep adding
more options.

Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>